/* Generated by the powerful Sio Tool
 * You can download the binary file here: https://github.com/Arapak/sio-tool
 * Author:  (Karol Bonat)
 * Time of creation: 2024-03-19 10:29:46
 * Notes: 
**/

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

typedef long long ll;

constexpr ll MAXN = 100005;

ll n, M;
ll m, f;

vector<ll> tabt[MAXN];
ll k[MAXN];



int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> n >> M;
	string s;
	for(ll i = 1; i <= M; i++){
		string t; 
		cin >> t >> k[i];
		for(char c : t){
			tabt[i].push_back(1-2*(c=='M'));
			m+=(c=='M')*k[i];
			// f+=(c=='F')*k[i];
		}
	}

	if(m > n){
		cout << "-1\n";
		return 0;
	}
    //Mother foka
    ll mf = n-m;
    ll c = 0;
	n*=2;
    ll pre=0;
    ll mp = 0;
    for(ll i = 1; i <= M; i++){
        ll dp = 0;
        ll md=0;
        for(ll j : tabt[i]){
            dp+=j;
            md = max(md, dp);
        }
        mp = max(mp, pre+md);
        pre += (k[i]-1)*dp;
        mp = max(mp, pre+md);
        pre += dp;
    }
    // cerr << mf << '\n';
    // cerr << mp << '\n';
    ll r = (mp- 2*mf);
    if((mp - r) % 2 == 0) r--;
    cout << max(0ll, r) << '\n';
	return 0;
}