qwq

#include<bits/stdc++.h>
using namespace std;
#define IT set<node>::iterator

struct node{
    unsigned l,r;
    char v;
    node(unsigned LEFT,unsigned RIGNT=0,char VALUE=0);
};
node::node(unsigned LEFT,unsigned RIGHT,char VALUE){
    l=LEFT;
    r=RIGHT;
    v=VALUE;
}
bool operator<(node a,node b){
	return a.l<b.l;
}
set<node>odt;
unsigned n,m;

inline IT split(unsigned p){
    IT it=odt.lower_bound(node(p));
    if(it!=odt.end()&&it->l==p)return it;
    --it;
    unsigned r=it->r,l=it->l;
    char v=it->v;
    odt.erase(it);
    odt.insert(node(l,p-1,v));
    return odt.insert(node(p,r,v)).first;
}
inline void assign(unsigned l,unsigned r,int v){
    IT itr=split(r+1),itl=split(l);
    odt.erase(itl,itr);
    odt.insert(node(l,r,v));
}
inline unsigned getcnt(unsigned l,unsigned r,char v){
    IT itr=split(r+1),itl=split(l);
    unsigned cnt=0;
    for(IT it=itl;it!=itr;++it)
        if(it->v==v)
            cnt+=it->r-it->l+1;
    return cnt;
}
inline void sortsec(unsigned l,unsigned r){
    IT itr=split(r+1),itl=split(l);
    unsigned cnt[26]={0};
    for(IT it=itl;it!=itr;++it)
        cnt[it->v-'A']+=it->r-it->l+1;    
    for(register unsigned i=0;i<26;++i){
        odt.insert(node(l,l+cnt[i],i+'A'));
        l+=cnt[i];
    }
}

int main(){
    scanf("%d%d",&n,&m);
    for(register unsigned i=1;i<=n;i++){
        char tmp;
        cin>>tmp;
        if(tmp>='a'&&tmp<='z')tmp-='a'-'A';
        odt.insert(node(i,i,tmp));
    }
    odt.insert(node(n+1,n+1,'\0'));
    for(register unsigned i=1;i<=m;i++){
        int t,l,r;
        char c;
        scanf("%d%d%d",&t,&l,&r);
        if(t==1||t==2)
            scanf("%c",c);
            
        if(t==1)
            printf("%u\n",getcnt(l,r,c));
        if(t==2)
            assign(l,r,c);
        if(t==3)
            sortsec(l,r);
    }
    return 0;
}