#include<bits/stdc++.h>
using namespace std;
long long n,m,k[100005],as,c[100005],b[100005],p,ss;
string s[100005];
int main(){
	freopen("Toilets.in","r",stdin);
	freopen("Toilets.out","w",stdout); 
    ios::sync_with_stdio(false);
    cin>>n>>m;
    for(long long i=1;i<=m;i++){
        cin>>s[i]>>k[i];
        long long s1=0,s2=0,ps=0;
		c[i]=-1e18;
        for(long long j=0;j<s[i].size();j++){
            if(s[i][j]=='M') s1++,ps++;
            else s2++;
            c[i]=max(c[i],s2-s1);
        }
        ss+=ps*k[i];
        b[i]=s2-s1;
    }
    if(ss!=n){
        cout<<"-1";
        return 0;
    }
    for(long long i=1;i<=m;i++){
        if(b[i]>0) as=max(as,p+b[i]*(k[i]-1ll)+c[i]);
        else as=max(as,p+c[i]);
        p+=b[i]*k[i];
    }
    cout<<as-1;
    return 0;
}