#include <bits/stdc++.h>
#define LLINF 100000000000000007

using namespace std;
typedef long long ll;
typedef string str;
template <typename T> using vec = vector<T>;

ll N, M, K;
ll f = 0, m = 0;
ll unsf = 0;
// female to move
ll ftm = 0;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	
	cin>>N>>M;

	vec<pair<str, ll>> movs;
	while(M--) {
		str s;
		cin>>s>>K;
		movs.push_back({s, K});
	}

	for(int j = movs.size() - 1; j >= 0; j--) {
		auto &[s, k] = movs[j];
		ll tf = 0;
		ll tm = 0;

		for(int i = s.size() - 1; i >= 0; i--) {
			if(s[i] == 'F') {
				if(m > 0) {
					m--;
					unsf = max(unsf, m);
				} else {
					f++;
				}
				tf++;
			} else {
				if(f > 0) {
					f--;
				}
				else {
					m++;
				}
				tm++;
			}
		}
		if(k == 1) continue;
		m += tm * (k - 2);
		f += tf * (k - 2);
		if(m >= f) {
			m -= f;
			f = 0;
		} else {
			f -= m;
			m = 0;
		}
		for(int i = s.size() - 1; i >= 0; i--) {
			if(s[i] == 'F') {
				if(m > 0) {
					m--;
					unsf = max(unsf, m);
				} else f++;
			} else {
				if(f > 0) f--;
				else m++;
			}
		}
		cout<<"m: "<<m<<" f: "<<f<<"\n";
	}

	if(m > 0) cout<<"-1";
	else cout<<unsf;
	
	
	cout.flush();
}