#include<bits/stdc++.h>
using namespace std;

int main(){
    long N, Q;
    string s;
    cin >> N >> Q >> s;
    long l = 0, r = N;
    vector<pair<char, long>> v(Q);
    for(auto& i : v){
        char c;
        cin >> i.first >> c;
        i.second = !(c & 2);
    }
    reverse(v.begin(), v.end());
    for(const auto& i : v){
        if(i.second){
            if(s[l] == i.first)++l;
            if(r < N && s[r] == i.first)++r;
        }else{
            if(l && s[l - 1] == i.first)--l;
            if(s[r - 1] == i.first)--r;
        }
    }
    cout << r - l << endl;
    return 0;
}