#include<cassert>
#include <bits/stdc++.h>
#ifndef IO_HPP
#define IO_HPP
#include<iostream>
#include<vector>
#include<queue>
#include<stack>
#include<array>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
using namespace std;
template<typename T1,typename T2>istream &operator>>(istream&,pair<T1,T2>&);
template<typename...Args>istream &operator>>(istream&,tuple<Args...>&a);
template<typename T>istream &operator>>(istream&is,vector<T>&a);
template<typename T,size_t N>istream &operator>>(istream&is,array<T,N>&a);
template<typename T1,typename T2>
istream &operator>>(istream&is,pair<T1,T2>&a){
  is>>a.first>>a.second;
  return is;
}
template<size_t pos,typename...Args>
void read_tuple(istream&is,tuple<Args...>&a){
  if constexpr(pos<tuple_size<tuple<Args...>>::value){
    is>>get<pos>(a);
    read_tuple<pos+1>(is,a);
  }
}
template<typename...Args>
istream &operator>>(istream&is,tuple<Args...>&a){
  read_tuple<0>(is,a);
  return is;
}
template<typename T>
istream &operator>>(istream&is,vector<T>&a){
  for(T&x:a)is>>x;
  return is;
}
template<typename T,size_t N>
istream &operator>>(istream&is,array<T,N>&a){
  for(T&x:a)is>>x;
  return is;
}
template<typename T1,typename T2>ostream &operator<<(ostream&os,const pair<T1,T2>&);
template<typename...Args>ostream &operator<<(ostream&os,const tuple<Args...>&);
template<typename T>ostream &operator<<(ostream&os,const vector<T>&);
template<typename T,typename Seq,typename Comp>ostream &operator<<(ostream&os,priority_queue<T,Seq,Comp>);
template<typename T>ostream &operator<<(ostream&os,queue<T>);
template<typename T>ostream &operator<<(ostream&os,deque<T>);
template<typename T>ostream &operator<<(ostream&os,stack<T>);
template<typename T,size_t N>ostream &operator<<(ostream&os,const array<T,N>&);
template<typename Key,typename Val,typename Comp>ostream &operator<<(ostream&os,const map<Key,Val,Comp>&);
template<typename Key,typename Val,typename Hash>ostream &operator<<(ostream&os,const unordered_map<Key,Val,Hash>&);
template<typename T,typename Comp>ostream &operator<<(ostream&os,const set<T,Comp>&);
template<typename T,typename Comp>ostream &operator<<(ostream&os,const multiset<T,Comp>&);
template<typename T,typename Hash>ostream &operator<<(ostream&os,const unordered_set<T,Hash>&);
template<typename T1,typename T2>
ostream &operator<<(ostream&os,const pair<T1,T2>&a){
  os<<a.first<<' '<<a.second;
  return os;
}
template<size_t pos,typename...Args>
void write_tuple(ostream&os,const tuple<Args...>&a){
  if constexpr(pos<tuple_size<tuple<Args...>>::value){
    if constexpr(pos>0)os<<' ';
    os<<get<pos>(a);
    write_tuple<pos+1>(os,a);
  }
}
template<typename...Args>
ostream &operator<<(ostream&os,const tuple<Args...>&a){
  write_tuple<0>(os,a);
  return os;
}
template<typename T>
ostream &operator<<(ostream&os,const vector<T>&a){
  os<<'{';
  for(int i=0;i<(int)a.size();i++){
    os<<a[i];
    if(i+1!=a.size())os<<',';
  }
  os<<'}';
  return os;
}
template<typename T,typename Seq,typename Comp>
ostream &operator<<(ostream&os,priority_queue<T,Seq,Comp>a){
  os<<'{';
  if(!a.empty()){
    os<<a.top();a.pop();
    while(!a.empty()){
      os<<',';
      os<<a.top();
      a.pop();
    }
  }
  os<<'}';
  return os;
}
template<typename T>
ostream &operator<<(ostream&os,queue<T>a){
  os<<'{';
  if(!a.empty()){
    os<<a.front();a.pop();
    while(!a.empty()){
      os<<',';
      os<<a.front();
      a.pop();
    }
  }
  os<<'}';
  return os;
}
template<typename T>
ostream &operator<<(ostream&os,deque<T>a){
  os<<'{';
  if(!a.empty()){
    os<<a.front();a.pop_front();
    while(!a.empty()){
      os<<',';
      os<<a.front();
      a.pop_front();
    }
  }
  os<<'}';
  return os;
}
template<typename T>
ostream &operator<<(ostream&os,stack<T>a){
  os<<'{';
  if(!a.empty()){
    os<<a.top();a.pop();
    while(!a.empty()){
      os<<',';
      os<<a.top();
      a.pop();
    }
  }
  os<<'}';
  return os;
}
template<typename T,size_t N>
ostream &operator<<(ostream&os,const array<T,N>&a){
  os<<'{';
  for(int i=0;i<(int)a.size();i++){
    os<<a[i];
    if(i+1!=a.size())os<<',';
  }
  os<<'}';
  return os;
}
template<typename Key,typename Val,typename Comp>
ostream &operator<<(ostream&os,const map<Key,Val,Comp>&a){
  if(a.empty()){
    os<<"{}";
    return os;
  }
  auto itr=a.begin();
  os<<"{["<<itr->first<<","<<itr->second<<']';
  while(++itr!=a.end())os<<",["<<itr->first<<','<<itr->second<<']';
  os<<'}';
  return os;
}
template<typename Key,typename Val,typename Hash>
ostream &operator<<(ostream&os,const unordered_map<Key,Val,Hash>&a){
  if(a.empty()){
    os<<"{}";
    return os;
  }
  auto itr=a.begin();
  os<<"{["<<itr->first<<","<<itr->second<<']';
  while(++itr!=a.end())os<<",["<<itr->first<<','<<itr->second<<']';
  os<<'}';
  return os;
}
template<typename T,typename Comp>
ostream &operator<<(ostream&os,const set<T,Comp>&a){
  if(a.empty()){
    os<<"{}";
    return os;
  }
  auto itr=a.begin();
  os<<'{'<<*itr;
  while(++itr!=a.end())os<<','<<*itr;
  os<<'}';
  return os;
}
template<typename T,typename Comp>
ostream &operator<<(ostream&os,const multiset<T,Comp>&a){
  if(a.empty()){
    os<<"{}";
    return os;
  }
  auto itr=a.begin();
  os<<'{'<<*itr;
  while(++itr!=a.end())os<<','<<*itr;
  os<<'}';
  return os;
}
template<typename T,typename Hash>
ostream &operator<<(ostream&os,const unordered_set<T,Hash>&a){
  if(a.empty()){
    os<<"{}";
    return os;
  }
  auto itr=a.begin();
  os<<'{'<<*itr;
  while(++itr!=a.end())os<<','<<*itr;
  os<<'}';
  return os;
}
#endif
using namespace std;
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int){for(auto &i:a)i--;}
using vref=typename vector<bool>::reference;
vref operator|=(vref a,bool b){a=a|b;return a;}
vref operator&=(vref a,bool b){a=a&b;return a;}
vref operator^=(vref a,bool b){a=a^b;return a;}
#define overload3(_1,_2,_3,name,...) name
#define rep1(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,l,r) for(int i=(int)(l);i<(int)(r);i++)
#define rep(...) overload3(__VA_ARGS__,rep2,rep1)(__VA_ARGS__)
#define reps(i,l,r) rep2(i,l,r)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcountll(x)
#define fin(x) return cout<<(x)<<'\n',static_cast<void>(0)
#define yn(x) cout<<((x)?"Yes\n":"No\n")
#define uniq(x) sort(all(x)),x.erase(unique(all(x)),x.end())
template<typename T>
inline int fkey(vector<T>&z,T key){return lower_bound(z.begin(),z.end(),key)-z.begin();}
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
#ifdef LOCAL
#include<debug.h>
#define SWITCH(a,b) (a)
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
#define SWITCH(a,b) (b)
#endif
struct Timer{
  clock_t start;
  Timer(){
    start=clock();
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout<<fixed<<setprecision(16);
  }
  inline double now(){return (double)(clock()-start)/1000;}
  #ifdef LOCAL
  ~Timer(){
    cerr<<"time:";
    cerr<<now();
    cerr<<"ms\n";
  }
  #endif
}timer;
void SOLVE();
int main(){
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
}
#include<type_traits>
#include<concepts>
template<typename T>
constexpr std::enable_if_t<std::numeric_limits<T>::digits<=32,int>msb(T n){return n==0?-1:31-__builtin_clz(n);}
template<typename T>
constexpr std::enable_if_t<(std::numeric_limits<T>::digits>32),int>msb(T n){return n==0?-1:63-__builtin_clzll(n);}

template<typename T>
constexpr std::enable_if_t<std::numeric_limits<T>::digits<=32,int>lsb(T n){return n==0?-1:__builtin_ctz(n);}
template<typename T>
constexpr std::enable_if_t<(std::numeric_limits<T>::digits>32),int>lsb(T n){return n==0?-1:__builtin_ctzll(n);}

template<typename T>
constexpr std::enable_if_t<std::is_integral_v<T>,T>floor_pow2(T n){return n==0?0:T(1)<<msb(n);}

template<typename T>
constexpr std::enable_if_t<std::is_integral_v<T>,T>ceil_pow2(T n){return n<=1?1:T(1)<<(msb(n-1)+1);}

template<std::integral T>
constexpr T safe_div(T a,T b){return a/b-(a%b&&(a^b)<0);}
template<std::integral T>
constexpr T safe_ceil(T a,T b){return a/b+(a%b&&(a^b)>0);}
template<typename M>
struct SegmentTree{
  using S=typename M::S;
private:
  int n,z;
  std::vector<S>dat;
public:
  SegmentTree():n(0),z(0),dat(){}
  explicit SegmentTree(int n):n(n),z(ceil_pow2(n)),dat(ceil_pow2(n)*2,M::e()){}
  explicit SegmentTree(const std::vector<S>&a):n(a.size()),z(ceil_pow2((int)a.size())){
    dat.resize(z*2,M::e());
    for(int i=0;i<n;i++)dat[i+z]=a[i];
    for(int i=z-1;i>=1;i--)dat[i]=M::op(dat[i*2],dat[i*2+1]);
  }
  SegmentTree(int n,S init):SegmentTree(std::vector<S>(n,init)){}
  inline S get(int i)const{return dat[i+z];}
  void set(int i,S x){
    assert(0<=i&&i<n);
    i+=z;
    dat[i]=x;
    i>>=1;
    while(i){
      dat[i]=M::op(dat[i*2],dat[i*2+1]);
      i>>=1;
    }
  }
  S prod(int l,int r)const{
    assert(0<=l&&l<=r&&r<=n);
    if(r==n)r=z;
    l+=z,r+=z;
    S left=M::e(),right=M::e();
    while(l<r){
      if(l&1)left=M::op(left,dat[l++]);
      if(r&1)right=M::op(dat[--r],right);
      l>>=1,r>>=1;
    }
    return M::op(left,right);
  }
  inline S all_prod()const{return dat[1];}
  template<typename Func>
  int max_right(int l,const Func&f)const{
    if(l==n)return n;
    l+=z;
    S now=M::e();
    do{
      while((~l)&1)l>>=1;
      S nxt=M::op(now,dat[l]);
      if(f(nxt))now=nxt,l++;
      else{
        while(l<z){
          l<<=1;
          nxt=M::op(now,dat[l]);
          if(f(nxt))now=nxt,l++;
        }
        return l-z;
      }
    }while(l!=(l&-l));
    return n;
  }
  template<typename Func>
  int min_left(int r,const Func&f)const{
    if(r==0)return 0;
    r+=z;
    S now=M::e();
    do{
      r--;
      while(r>1&&(r&1))r>>=1;
      S nxt=M::op(dat[r],now);
      if(f(nxt))now=nxt;
      else{
        while(r<z){
          r=(r<<1)+1;
          nxt=M::op(dat[r],now);
          if(f(nxt))now=nxt,r--;
        }
        return r-z+1;
      }
    }while(r!=(r&-r));
    return 0;
  }
  friend std::ostream &operator<<(std::ostream &os,const SegmentTree&seg){
    os<<"{";
    for(int i=0;i<seg.n;i++)os<<seg.dat[i+seg.z]<<",}"[i+1==seg.n];
    if(seg.n==0)os<<"}";
    return os;
  }
};
template<typename T,bool MIN=true>
struct min_plus_semiring{
private:
  T v;
public:
  min_plus_semiring():v(0){}
  min_plus_semiring(T v):v(v){}
  static constexpr bool comp(T a,T b){
    if constexpr(MIN)return a<b;
    else return a>b;
  }
  static constexpr T zero(){
    if constexpr(MIN)return std::numeric_limits<T>::max()/2;
    else return std::numeric_limits<T>::min()/2;
  }
  static constexpr T one(){return 0;}
  T val()const{return v;}
  min_plus_semiring &operator+=(const min_plus_semiring&b){
    if(comp(b.v,v))v=b.v;
    return *this;
  }
  min_plus_semiring &operator*=(const min_plus_semiring&b){
    v+=b.v;
    return *this;
  }
  friend min_plus_semiring operator+(const min_plus_semiring&a,const min_plus_semiring&b){return min_plus_semiring(a)+=b;}
  friend min_plus_semiring operator*(const min_plus_semiring&a,const min_plus_semiring&b){return min_plus_semiring(a)*=b;}
  friend std::istream &operator>>(std::istream&is,min_plus_semiring&b){
    is>>b.v;
    return is;
  }
  friend std::ostream &operator<<(std::ostream&os,const min_plus_semiring&b){
    os<<b.v;
    return os;
  }
  auto operator<=>(const min_plus_semiring&)const=default;
};
template<typename T,int N,int M=N>
struct ConstantMatrix{
private:
  std::array<std::array<T,M>,N>dat;
  static constexpr T zero(){
    if constexpr(requires(){T::zero();})return T::zero();
    else return T(0);
  }
  static constexpr T one(){
    if constexpr(requires(){T::one();})return T::one();
    else return T(1);
  }
public:
  ConstantMatrix():ConstantMatrix(T()){}
  explicit ConstantMatrix(T x){
    dat.fill([&x](){std::array<T,M>res;res.fill(x);return res;}());
  }
  static ConstantMatrix E(){
    static_assert(N==M);
    ConstantMatrix res(zero());
    for(int i=0;i<N;i++)res[i][i]=one();
    return res;
  }
  inline  ConstantMatrix &operator+=(const ConstantMatrix&rhs){
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)(*this)[i][j]+=rhs[i][j];
    return *this;
  }
  inline ConstantMatrix &operator-=(const ConstantMatrix&rhs){
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)(*this)[i][j]-=rhs[i][j];
    return *this;
  }
  inline ConstantMatrix &operator*=(const ConstantMatrix&rhs){
    static_assert(N==M);
    ConstantMatrix res;
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)for(int k=0;k<M;k++)res[i][k]+=(*this)[i][j]*rhs[j][k];
    (*this)=std::move(res);
    return *this;
  }
  friend ConstantMatrix operator+(const ConstantMatrix&lhs,const ConstantMatrix&rhs){return ConstantMatrix(lhs)+=rhs;}
  friend ConstantMatrix operator-(const ConstantMatrix&lhs,const ConstantMatrix&rhs){return ConstantMatrix(lhs)-=rhs;}
  template<int K>friend ConstantMatrix<T,N,K> operator*(const ConstantMatrix&lhs,const ConstantMatrix<T,M,K>&rhs){
    ConstantMatrix<T,N,K>res(zero());
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)for(int k=0;k<K;k++)res[i][k]+=lhs[i][j]*rhs[j][k];
    return res;
  }
  std::array<T,M> &operator[](int i){return dat[i];}
  const std::array<T,M> &operator[](int i)const{return dat[i];}
  friend bool operator==(const ConstantMatrix&lhs,const ConstantMatrix&rhs){
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)if(lhs[i][j]!=rhs[i][j])return false;
    return true;
  }
  friend bool operator!=(const ConstantMatrix&lhs,const ConstantMatrix&rhs){
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)if(lhs[i][j]!=rhs[i][j])return true;
    return false;
  }
  T det()const{
    static_assert(N==M);
    T res=1;
    ConstantMatrix mat(*this);
    for(int i=0;i<M;i++){
      int idx=-1;
      for(int j=i;j<N;j++)if(mat[j][i]!=T()){
        idx=j;
        break;
      }
      if(idx==-1)return T();
      if(i!=idx)std::swap(mat[i],mat[idx]),res=-res;
      res*=mat[i][i];
      T inv_ii=mat[i][i].inv();
      for(int j=i+1;j<M;j++)mat[i][j]*=inv_ii;
      for(int j=i+1;j<N;j++){
        T coef=-mat[j][i];
        for(int k=i+1;k<M;k++)mat[j][k]+=coef*mat[i][k];
      }
    }
    return res;
  }
  ConstantMatrix inv()const{
    static_assert(N==M);
    ConstantMatrix res=E(),mat=(*this);
    for(int i=0;i<N;i++){
      int id=-1;
      for(int j=i;j<N;j++)if(mat[j][i]!=T()){
        id=j;
        break;
      }
      if(id==-1)return ConstantMatrix();
      if(i!=id){
        std::swap(mat[i],mat[id]);
        std::swap(res[i],res[id]);
      }
      T inv=mat[i][i].inv();
      for(int j=0;j<N;j++)if(i!=j){
        T x=mat[j][i];
        for(int k=0;k<N;k++){
          mat[j][k]-=mat[i][k]*x;
          res[j][k]-=res[i][k]*x;
        }
      }
    }
    return res;
  }
  template<std::integral U>
  ConstantMatrix pow(U k)const{
    static_assert(N==M);
    ConstantMatrix res=ConstantMatrix::E(),a(*this);
    while(k){
      if(k&1)res*=a;
      a*=a;
      k>>=1;
    }
    return res;
  }
  std::vector<std::vector<T>>to_vector()const{
    std::vector<std::vector<T>>res(N,std::vector<T>(M));
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)res[i][j]=dat[i][j];
    return res;
  }
  friend std::istream &operator>>(std::istream&is,ConstantMatrix&rhs){
    for(int i=0;i<N;i++)for(int j=0;j<M;j++)is>>rhs[i][j];
    return is;
  }
  friend std::ostream &operator<<(std::ostream &os,const ConstantMatrix&rhs){
    for(int i=0;i<N;i++){
      for(int j=0;j<M;j++)os<<rhs[i][j]<<" \n"[j+1==M];
    }
    return os;
  }
};
struct M{
  using S=ConstantMatrix<min_plus_semiring<int>,4>;
  static S op(S x,S y){return x*y;}
  static S e(){return S::E();}
};
void SOLVE(){
  int n,q;
  cin>>n>>q;
  string s;
  cin>>s;
  auto get=[](char c)->M::S {
    M::S res;
    rep(i,4)rep(j,4){
      if(i<=j){
        res[i][j]=c==j+'A'?0:1;
      }
      else res[i][j]=1e9;
    }
    return res;
  };
  vector<M::S>init(n);
  rep(i,n)init[i]=get(s[i]);
  SegmentTree<M>seg(init);
  while(q--){
    int t;
    cin>>t;
    if(t==1){
      int x;
      char c;
      cin>>x>>c;
      x--;
      seg.set(x,get(c));
    }
    else{
      int l,r;
      cin>>l>>r;
      l--;
      auto mat=seg.prod(l,r);
      int ans=1e9;
      rep(i,4)rep(j,4)chmin(ans,mat[i][j].val());
      cout<<ans<<'\n';
    }
  }
}