#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main() {
  int n;
  cin >> n;
  if (n == 2) {
    cout << 1 << endl;
    return 0;
  }

  vector<int> t(n - 2), s(n - 2), d(n - 2);
  int cd = 1;
  string cur;
  cin >> cur;
  int single_idx = -1;
  for (int i = 0; i < n - 2; i++) {
    cin >> cur;
    for (int j = 0; j < cur.length() - 1; j++) {
      if (cur[j] == 't') t[i]++; else s[i]++;
    }
    if (cur[cur.length() - 1] == '{') d[i] = cd++; else d[i] = --cd;
    if (d[i] == 1) single_idx = i;
  }

  if (single_idx == -1) {
    cout << 1 << endl;
    return 0;
  }

  for (int ans = 1; ans <= 1000; ans++) {
    int k = t[single_idx] * ans + s[single_idx];
    bool ok = true;
    for (int i = 0; i < n - 2; i++) {
      if (t[i] * ans + s[i] != d[i] * k) {
        ok = false;
        break;
      }
    }
    if (ok) {
      cout << ans << endl;
      return 0;
    }
  }

  cout << -1 << endl;
  return 0;
}