#include<bits/stdc++.h>
using namespace std;
#include<atcoder/segtree>
#define q int
#define c(i,v,n)for(q i=v;i<n;i++)
struct S{q D[4][4];S(){c(i,0,4)c(j,0,4)D[i][j]=0;}S(q x){c(i,0,4)c(j,0,4)D[i][j]=(i<=x&&x<=j?0:1);}};
S o(S L,S R){S K;c(i,0,4)c(j,i,4){K.D[i][j]=1e9;c(k,i,j+1)K.D[i][j]=min(K.D[i][j],L.D[i][k]+R.D[k][j]);}return K;}
S e(){return S();}
int main() {
    q N,Q,p,l;string T;cin>>N>>Q>>T;
    vector<S>A(N);c(i,0,N)A[i]=S(T[i]-'A');
    atcoder::segtree<S,o,e>g(A);
    while(Q--){
    	cin>>p;
    	if(--p){
    		cin>>p>>l;
    		cout<<g.prod(p-1,l).D[0][3]<<endl;
    	}
    	else {
    		char c;cin>>l>>c;
    		g.set(l-1,S(c-'A'));
    	}
    }
}