// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx2,tune=native")

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <locale>
#include <map>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <unordered_set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <utility>
#include <valarray>
#include <vector>
#include <cstring>
#include <unordered_map>
#include <cmath>
#include <array>
#include <cassert>
#include <random>
#include <chrono>

using namespace std;

#define          BIT(i,j)  (((i)>>(j))&1LL)
#define           MASK(i)  (1LL<<(i))
#define            ALL(x)  (x).begin(),(x).end()
#define             SZ(x)  (int)(x).size()
#define                fi  first
#define                se  second
#define               ull  ungsigned long long
#define                ll  long long
#define                ld  long double
#define                vi  vector<int>
#define               vvi  vector<vi>
#define              vvvi  vector<vvi>
#define               pii  pair<int,int>
#define              vpii  vector<pii>
#define             vvpii  vector<vpii>
#define REPDIS(i,be,en,j)  for(int i = (be); i<=(en); i+=j)
#define     REPD(i,be,en)  for(int i = (be); i>=(en); i--)
#define      REP(i,be,en)  for(int i = (be); i<=(en); i++)
#define              endl  "\n"
#define                MP  make_pair
// #define               int  ll

//-----------------------------------------------------------------------------------------------//
inline void scan(){} template<typename F, typename... R> inline void scan(F &f,R&... r){cin>>f;scan(r...);}
inline void print(){} template<typename F, typename... R> inline void print(F f,R... r){cout<<f;print(r...);}
//-----------------------------------------------------------------------------------------------//

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
//------------------------------------------------------------------------------------------------//
const  ll   LINF = 1e18;
const int    INF = 1e9;
const int    LOG = 20;
const int   MAXN = 2e5+7;
const int      N = 1e2+3;
const int    MOD = 1e9+7;
const int   BASE = 1e5;
const  ld    EPS = 1e-9;
const  ld     PI = acos(-1);
const int OFFSET = 1e3;
//------------------------------------------------------------------------------------------------//
template<typename T1, typename T2> bool mini(T1 &a, T2 b){if(a>b){a=b;return true;}return false;}
template<typename T1, typename T2> bool maxi(T1 &a, T2 b){if(a<b){a=b;return true;}return false;}
template<typename T> T gcd(T a, T b) { while(b) { a %= b; swap(a,b); } return a; }
template<typename T> T lcm(T a, T b) { return a/gcd(a,b)*b; }
//------------------------------------------------------------------------------------------------//

/*
----------------------------------------------------------------
    END OF TEMPLATE
----------------------------------------------------------------
*/

int a[MAXN];

struct node {
    vvi f;

    node() {
        f.assign(4,vi(4,INF));
    }

    node operator + (const node& other) {
        node res;
        for (int i = 0; i<4; i++) {
            for (int j = i; j<4; j++) {
                for (int k = i; k<=j; k++) {
                    mini(res.f[i][j],f[i][k]+other.f[k][j]);
                }
            }
        }
        return res;
    }
};

node tam;

struct segment_tree {
    vector<node> st;
    int n;

    void build(int id, int l, int r) {
        if (l==r) {
            for (int i = 0; i<4; i++) {
                for (int j = i; j<4; j++) {
                    int val = (a[l]<i || a[l]>j)?1:0;
                    st[id].f[i][j] = val;
                }
            }
            return ;
        }
        int mid = (l+r)>>1;
        build(id<<1,l,mid);
        build(id<<1|1,mid+1,r);
        st[id] = st[id<<1]+st[id<<1|1];
    }

    void update(int id, int l, int r, int pos, int c) {
        if (l>pos || r<pos) return ;
        if (l==r) {
            for (int i = 0; i<4; i++) {
                for (int j = i; j<4; j++) {
                    int val = (c<i || c>j);
                    st[id].f[i][j] = val;
                }
            }
            return ;
        }
        int mid = (l+r)>>1;
        update(id<<1,l,mid,pos,c);
        update(id<<1|1,mid+1,r,pos,c);
        st[id] = st[id<<1]+st[id<<1|1];
    }

    node get(int id, int l, int r, int lo, int hi) {
        if (l>=lo && r<=hi) return st[id];
        int mid = (l+r)>>1;
        if(hi<=mid){
            return get(id<<1,l,mid,lo,hi);
        }else{
            if(lo>mid){
                return get(id<<1|1,mid+1,r,lo,hi);
            }else{
                node p1 = get(id<<1,l,mid,lo,min(mid,hi));
                node p2 = get(id<<1|1,mid+1,r,max(mid+1,lo),hi);
                return p1+p2;
            }
        }
        // cerr << l << " " << r << " " << lo << " " << hi << endl;
        // cerr << "WA" << endl;
        return tam;
    }

    void update(int pos, int c) {
        update(1,1,n,pos,c);
    }

    node get(int l, int r) {
        return get(1,1,n,l,r);
    }

    segment_tree(int _n):n(_n){
        st.assign(4*n,node());
    }
};

int tran(char ch) {
    return ch-'A';
}

void solve() {
    int n,q; cin >> n >> q;
    string s; cin >> s;
    for (int i = 0; i<n; i++)  a[i+1] = tran(s[i]);
    segment_tree seg(n);
    seg.build(1,1,n);
    while (q--) {
        int op; cin >> op;
        if (op==1) {
            int x; cin >> x;
            char c; cin >> c;
            a[x] = tran(c);
            seg.update(x,tran(c));
        }else {
            int l,r; cin >> l >> r;
            cout << seg.get(l,r).f[0][3] << endl;
        }
    }
}

signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    #define task "test"
    if(fopen(task".inp","r")){
        freopen(task".inp","r",stdin);
        freopen(task".out","w",stdout);
    }
    #define task1 "nothing"
    if(fopen(task1".inp","r")){
        freopen(task1".inp","r",stdin);
        freopen(task1".out","w",stdout);
    }

    int test = 1;

    while(test--){
        solve();
    }
    cerr << "\nTime elapsed: " << 1000*clock()/CLOCKS_PER_SEC << "ms\n";
    return 0;
}

/**  /\_/\
 *  (= ._.)
 *  / >TL \>AC
**/