#include <bits/stdc++.h>
using namespace std;
#define st first
#define nd second
#define pb push_back
typedef long long ll;
const int N = 2e5+3;
ll suf[N];
vector<pair<string, ll>> parts;
int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	ll n, mc=0;
	ll m, x, out=0;
	cin >> n >> m;
	for(int i=0; i<m; i++){
		string s;
		cin >> s >> x;
		parts.pb({s, x});
	}
	ll lst=0;
	for(int i=m-1; i>=0; i--){
		int ln=parts[i].st.size();
		ll tmpMc=0, mn=0;
		suf[ln]=lst;
		for(int j=ln-1; j>=0; j--){
			suf[j]=suf[j+1];
			if(parts[i].st[j]=='M'){
				tmpMc++;
				suf[j]--;
			}else suf[j]++;
			mn=min(mn, suf[j]);
		}
		tmpMc*=parts[i].nd;
		mn*=parts[i].nd;
		lst=suf[0]*x;
		mc+=tmpMc;
		out=min(out, mn);
	}
	if(mc>n){
		cout << -1 << '\n';
		return 0;
	}
	out*=(-1);
	out--;
	cout << out << '\n';
	return 0;
}