#include <bits/stdc++.h>
#include <atcoder/all>
using mint = atcoder::static_modint<998244353>;
//using mint = atcoder::static_modint<1000000007>;
using namespace std;
using namespace atcoder;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<n; i++)
const vector<int> dx{1,0,-1,0},dy{0,1,0,-1};

struct P{
    int a[4][4];
    P(){
        rep(i,0,4)rep(j,0,4)a[i][j]=0;
    }
};

P convert(char c){
    P z;
    rep(i,0,4)rep(j,i,4){
        if(i<=c-'A' && c-'A'<=j)z.a[i][j]=0;
        else z.a[i][j]=1;
    }
    return z;
}
P op(P x,P y){
    P z;
    rep(i,0,4)rep(j,i,4)z.a[i][j]=1e9;
    rep(i,0,4)rep(j,i,4)rep(k,j,4){
        z.a[i][k]=min(z.a[i][k],x.a[i][j]+y.a[j][k]);
    }
    return z;
}
P e(){return P();}

int main(){
    int n,Q;
    cin >> n >> Q;
    string s;
    cin >> s;
    segtree<P,op,e> seg(n);
    rep(i,0,n)seg.set(i,convert(s[i]));

    vector<int> out;
    rep(q,0,Q){
        int t;cin >> t;
        if(t==1){
            int x;cin >> x;
            char c;cin >> c;
            seg.set(x-1,convert(c));
            continue;
        }
        int l,r;
        cin >> l >> r;
        l--;
        auto p=seg.prod(l,r);
        out.push_back(p.a[0][3]);
    }
    for(auto x:out)cout << x << "\n";
}