#include <iostream>
using namespace std;

int main() {
  int n;
  cin >> n;
  int res = 0;
  for (int i = 0; i < n; ++i) {
    int H, M, h, m;
    char tmp;
    cin >> H >> tmp >> M >> h >> tmp >> m;
    int T = 60 * H + M, t = 60 * h + m;
    res += T < t ? t - T : 24 * 60 - T + t;
  }
  cout << res << endl;
  return 0;
}