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

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<vector<int> > mati;
typedef vector<vector<double> > matd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;
typedef vector<pll> vpll;

#define FOR(i,x,y) for(ll i=(ll)x; i<(ll)y; ++i)
#define REP(i,y) FOR(i, 0, y)
#define RFOR(i,x,y) for(ll i=(ll)x; i>=(ll)y; --i)
#define RREP(i,x) RFOR(i, x, 0)
#define ALL(a) a.begin(), a.end()
#define pb push_back

inline void IN(void){
  return;
}

template <typename First, typename... Rest>
void IN(First& first, Rest&... rest){
  cin >> first;
  IN(rest...);
  return;
}

inline void OUT(void){
  cout << "\n";
  return;
}

template <typename First, typename... Rest>
void OUT(First first, Rest... rest){
  cout << first << " ";
  OUT(rest...);
  return;
}

template <typename T>
void vec_print(vector<T> VEC){
  REP(i, VEC.size()){
    cout << VEC[i] << " ";
  }
  cout << "\n";
};

template <typename T>
void mat_print(vector<vector<T> > MAT){
  REP(i, MAT.size()){
    REP(j, MAT[i].size()){
      cout << MAT[i][j] << " ";
    }
    cout << "\n";
  }
};

template <typename CLASS1, typename CLASS2>
class HOGE{
  public:
    CLASS1 key;
    CLASS2 value;
    HOGE(void){
      return;
    };
    HOGE(CLASS1 key, CLASS2 value){
      this->key = key;
      this->value = value;
    };
    ~HOGE(void){
      return;
    };

    void print(void){
      cout << "key : " << key << ", value : " << value << "\n";
      return;
    };
    
    bool operator==(const HOGE &obj){
      return (this->value == obj.value);
    };
    bool operator<(const HOGE &obj){
      return (this->value < obj.value);
    };
    bool operator>(const HOGE &obj){
      return (this->value > obj.value);
    };
};

template <typename CLASS1, typename CLASS2>
bool operator==(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value == hoge2.value;
};

template <typename CLASS1, typename CLASS2>
bool operator<(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value < hoge2.value;
};

template <typename CLASS1, typename CLASS2>
bool operator>(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value > hoge2.value;
};

constexpr int INF = (1<<30);
constexpr ll INFLL = 1LL<<62;
constexpr long double EPS = 1e-12;
constexpr ll MOD = (ll)((1E+9)+7);

ll N, Q;
string str;
vector<char> t, d;

bool right_fall_flag(ll pos){
  for(int i=0; i<Q; ++i){
    if(str[pos] == t[i]){
      if(d[i]=='R'){
        pos++;
        if(pos>=N) return true;
      }else{
        pos--;
        if(pos<0) return false;
      }
    }
  }
  return false;
}

bool left_fall_flag(ll pos){
  for(int i=0; i<Q; ++i){
    if(str[pos] == t[i]){
      if(d[i]=='R'){
        pos++;
        if(pos>=N) return false;
      }else{
        pos--;
        if(pos<0) return true;
      }
    }
  }
  return false;
}

ll right_search(void){
  ll left = 0;
  ll right = N-1;
  if(right_fall_flag(left)) return 0;
  if(!right_fall_flag(right)) return N;
  while(right-left>1){
    ll mid = (left+right)/2;
    if(right_fall_flag(mid)) right = mid;
    else left = mid;
  }
  if(right_fall_flag(left)) return left;
  return right;
}

ll left_search(void){
  ll left = 0;
  ll right = N-1;
  if(!left_fall_flag(left)) return -1;
  if(left_fall_flag(right)) return N-1;
  while(right-left>1){
    ll mid = (left+right)/2;
    if(left_fall_flag(mid)) left = mid;
    else right = mid;
  }
  if(left_fall_flag(right)) return right;
  return left;
}

int main(){
  cin.tie(0); // cut the cin and cout (default, std::flush is performed after std::cin)
  ios::sync_with_stdio(false); // cut the iostream and stdio (DON'T endl; BUT "\n";)

  IN(N,Q);
  IN(str);
  t.resize(Q);
  d.resize(Q);
  REP(i,Q) IN(t[i], d[i]);

  //REP(i,N) OUT(i,right_fall_flag(i),left_fall_flag(i));

  ll right_min = right_search();
  ll left_max = left_search();

  //OUT(left_max, right_min);

  OUT(max(N-((N-right_min)+(left_max+1)), (ll)0));

  return 0;
}

Measured memory_bytes: 976