#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
int main()
{
// speed up std::cin & std::cout
std::ios::sync_with_stdio(false);
long long N;
int M;
std::vector<std::string> S;
std::vector<long long> K;
std::cin >> N >> M;
for(int i = 0; i < M; ++i) {
std::string S_i;
long long K_i;
std::cin >> S_i >> K_i;
S.push_back(S_i);
K.push_back(K_i);
}
long long minimum = 0;
long long global_count = 0;
for(int section = M - 1; section >= 0; --section) {
const std::string& S_i = S[section];
const long long K_i = K[section];
int local_count = 0, diff_minimum = 0;
for(int index = S_i.size() - 1; index >= 0; --index) {
const char c = S_i[index];
local_count += (c == 'F' ? 1 : -1);
diff_minimum = std::min(diff_minimum, local_count);
}
const long long candidate_first = global_count + diff_minimum;
const long long candidate_last = global_count + (K_i - 1) * local_count
+ diff_minimum;
minimum = std::min(minimum, std::min(candidate_first, candidate_last));
global_count += local_count * K_i;
}
long long answer;
// global_count = |female| - |male|
if(global_count < 0) {
answer = -1;
} else {
if(minimum >= -1) {
answer = 0;
} else {
answer = -(minimum + 1);
}
}
std::cout << answer << std::endl;
return 0;
}
