#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;}};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();}main(){q N,Q,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>>N;if(--N){cin>>N>>l;cout<<g.prod(N-1,l).D[0][3]<<endl;}else{char c;cin>>l>>c;g.set(l-1,S(c-'A'));}}}