#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(), v.end()
#define sz(v) (int)v.size()
#define ov4(a, b, c, d, name, ...) name
#define rep3(i, a, b, c) for (int i = (a); i < (b); i += (c))
#define rep2(i, a, b) rep3(i, a, b, 1)
#define rep1(i, n) rep2(i, 0, n)
#define rep0(n) rep1(aaaaaa, n)
#define rep(...) ov4(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define per(i, a, b) for(int i = (a)-1; i >= (b); i--) 
#define fore(e, v) for (auto&& e : v)
#define lb(v, x) (lower_bound(all(v), x)- begin(v));
#define eb emplace_back


using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using ld = double;

template<class T, class S> bool chmin(T& a, const S& b) {return a > b ? a = b, 1 : 0; }
template<class T, class S> bool chmax(T& a, const S& b) {return a < b ? a = b, 1 : 0; }

vector<int> dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};

const int INF = 1e9 + 100;
const ll linf = 1e18 + 100;
int clamp(int l, int r, int x) {return min(max(l, x), r);}

template<class S, S (*op)(S, S), S (*e)()> struct segtree {
   segtree(int n) : segtree(vector<S>(n, e())) {}
   segtree(const vector<S>& v) : n(sz(v)) {
      s = bit_ceil(unsigned(n));
      log = countr_zero(unsigned(s));
      d = vector<S>(2 * s, e());
      rep(i, n) d[s + i] = v[i];
      per(i, s, 1) update(i);
   }
   void set(int p, S x) {
      d[p += s] = x;
      rep(i, 1, log + 1) update(p >> i);
   }
   S prod(int l, int r) const {
      S sml = e(), smr = e();
      l += s, r += s;
      while(l < r) {
         if(l & 1) sml = op(sml, d[l++]);
         if(r & 1) smr = op(d[--r], smr);
         l >>= 1, r >>= 1;
      }
      return op(sml, smr);
   }
   S all_prod() const { return d[1]; }
   template<typename F> int max_right(int l, F f) const {
      if(l == n) return n;
      l += s;
      S sm = e();
      do {
         while(~l & 1) l >>= 1;
         if(!f(op(sm, d[l]))) {
            while(l < s) {
               l <<= 1;
               if(f(op(sm, d[l]))) sm = op(sm, d[l++]);
            }
            return l - s;
         }
         sm = op(sm, d[l++]);
      } while((l & -l) != l);
      return n;
   }
   template<typename F> int min_left(int r, F f) const {
      if(!r) return 0;
      r += s;
      S sm = e();
      do {
         r--;
         while(r > 1 and r & 1) r >>= 1;
         if(!f(op(d[r], sm))) {
            while(r < s) {
               r = (2 * r + 1);
               if(f(op(d[r], sm))) sm = op(d[r--], sm);
            }
            return r + 1 - s;
         }
         sm = op(d[r], sm);
      } while((r & -r) != r);
      return 0;
   }

   private:
   int n, s, log;
   vector<S> d;
   void update(int k) { d[k] = op(d[k * 2], d[k * 2 + 1]); }
};

const int iinf = 1e9 + 100;

using S = array<int, 25>;
const int m = 4;



int idx(int l, int r){
    return l * (m + 1) + r;
}

void print(S x) {
    rep(l, m+1) {
        rep(r, l+1, m+1) cout << x[idx(l, r)] << " ";
        cout << endl;
    }
}
S e() {
    return S{};   
}

S op(S x, S y) {
    S z = e();
    rep(l, m)rep(r, l+1, m+1)z[idx(l, r)] = iinf;
    rep(l, m+1)rep(r, l+1, m+1)rep(k, l, r) {
        chmin(z[idx(l, r)], x[idx(l, k+1)] + y[idx(k, r)]);
    }
    return z;
}


void solve() {
    int n, q;cin >> n >> q;
    string s;cin >> s;
    

    auto item = [&](int x) -> S {
        S z = e();
        rep(l, m)rep(r, l+1, m+1)z[idx(l, r)] = iinf;
        rep(l, m)rep(r, l+1, m+1) {
            if (x < l) z[idx(l, r)] = 1;
            else if (x >= r) z[idx(l, r)] = 1;
            else z[idx(l, r)] = 0;
        }
        return z;
    };

    vector<S> v(n);
    rep(i, n) v[i] = item(s[i] - 'A');
    segtree<S, op, e> st(v);

    rep(q) {
        int t;cin >> t;
        if (t == 1) {
            int x;cin >> x;x--;
            char c;cin >> c;
            st.set(x, item(c - 'A'));
        }
        else {
            int l, r;cin >> l >> r;
            l--;
            // print(st.prod(l, r));
            cout << st.prod(l, r)[idx(0, m)] << endl;
        }

    }
}

int main() {
    
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
    // int T;cin >> T;
    int T = 1;
    while (T--) {
        solve();
    }
}