#include <bits/stdc++.h>
using namespace std;
int main(void){
  int n;
  cin >> n;
  int answer=0;
  for(int i=0;i<n;i++){
    int ah,am,bh,bm;
    char c;
    cin >> ah >>c>> am >> bh >>c>> bm;
    answer+=(bh*60+bm+1440-ah*60-am)%1440;
  }
  cout << answer << endl;
  return 0;
}