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

int main() {
  int N;
  cin >> N;
  int sum = 0;
  for (int i = 0; i < N; i++) {
    int hh, mm, h, m;
    char sep;
    cin >> hh >> sep >> mm >> h >> sep >> m;
    mm += hh * 60;
    m += h * 60;
    if (mm < m) sum += m - mm;
    else sum += m + 24 * 60 - mm;
  }
  printf("%d\n", sum);
  return 0;
}