#include <bits/stdc++.h>

using namespace std;

int main()
{
  int N;
  scanf("%d", &N);
  int minute = 0;
  while(N--) {
    int h1, m1, h2, m2;
    scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
    if(make_pair(h1, m1) > make_pair(h2, m2)) minute += 1440 - h1 * 60 - m1 + h2 * 60 + m2;
    else minute += h2 * 60 + m2 - h1 * 60 - m1;
  }
  cout << minute << endl;
}