#include <iostream>

using namespace std;

int main() {
  int n, sumH=0, sumM=0;
  cin >> n;
  for (int i=0; i<n; i++) {
    int H, M, h, m;
    scanf("%d:%d %d:%d", &H, &M, &h, &m);
    if (H>h) {
      sumH+=24-(H+1)+h;
      sumM+=60-M+m;
    } else {
      sumH+=h-H-1;
      sumM+=60-M+m;
    }
  }

  cout << sumH*60+sumM << endl;
  return 0;
}