#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  cin >> N;

  int ans = 0;
  for (int i = 0; i < N; i++) {
    int a, b, c, d;
    char e;
    cin >> a >> e >> b >> c >> e >> d;
    int x = a * 60 + b;
    int y = c * 60 + d;
    ans += (x < y) ? y - x : y - x + 1440;
  }

  cout << ans << "\n";
}