#include <iostream>
using namespace std;

int main() {
  int H, M, h, m, n, ans = 0;
  char d;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> H >> d >> M >> h >> d >> m;
    if (H > h || (H == h && M > m)) h += 24;
    ans += (h * 60 + m) - (H * 60 + M);
  }
  cout << ans << endl;
  return 0;
}