#include <bits/stdc++.h>
using namespace std;
int n,m,s,k;
int main(){
	freopen("Toilets.in","r",stdin);
	freopen("Toilets.out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
    cin>>n>>m;
    int boy=0,girl=0,k;
    string s;
    for(int i=1;i<=m;i++){
        cin>>s>>k;
        for(int i=0;i<s.size();i++){
            if(s[i]=='F') girl+=k;
            else boy+=k;
        }
    }
    if(boy>girl){
        cout<<-1<<endl;
        return 0;
    }
}