#include <bits/stdc++.h>
using namespace std;
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using LL = long long;
using VL = vector<LL>;
using VVL = vector<VL>;
using PLL = pair<LL, LL>;
using VS = vector<string>;
template <class S, class T>
istream& operator>>(istream& is, pair<S, T>& p) {
  return is >> p.first >> p.second;
}
template <class T>
istream& operator>>(istream& is, vector<T>& xs) {
  for (auto& x : xs) is >> x;
  return is;
}
template <class S, class T>
ostream& operator<<(ostream& os, const pair<S, T>& p) {
  return os << p.first << " " << p.second;
}
template <class T>
ostream& operator<<(ostream& os, const vector<T>& xs) {
  for (unsigned int i = 0; i < xs.size(); ++i) os << (i ? " " : "") << xs[i];
  return os;
}
template <class T>
void maxi(T& x, T y) {
  if (x < y) x = y;
}
template <class T>
void mini(T& x, T y) {
  if (x > y) x = y;
}
void debug(istringstream&) {}
template <char sep = ',', class Head, class... Tail>
void debug(istringstream& iss, Head&& head, Tail&&... tail) {
  string name;
  getline(iss, name, ',');
  cout << sep << name << "=" << head;
  debug(iss, forward<Tail>(tail)...);
}
const double EPS = 1e-10;
const double PI = acos(-1.0);
const LL MOD = 1e9 + 7;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  int N, Q;
  cin >> N >> Q;
  string S;
  cin >> S;
  vector<pair<char, char>> qs(Q);
  cin >> qs;
  int l = -1, r = N;
  for (int i = Q - 1; i >= 0; --i) {
    char tc = qs[i].first;
    if (qs[i].second == 'L') {
      if (l + 1 >= N) continue;
      char c = S[l + 1];
      if (c == tc) ++l;
    } else {
      if (r - 1 < 0) continue;
      char c = S[r - 1];
      if (c == tc) --r;
    }
  }
  if (l >= N || r < 0 || l >= r) {
    cout << 0 << endl;
  } else
    cout << (r - l - 1) << endl;
  return 0;
}
