#include <bits/stdc++.h>
using namespace std;
int main(){
  int N;
  cin >> N;
  int ans = 0;
  for (int i = 0; i < N; i++){
    int H1, M1, h1, m1;
    char c1, c2;
    cin >> H1 >> c1 >> M1 >> h1 >> c2 >> m1;
    int t1 = H1 * 60 + M1;
    int t2 = h1 * 60 + m1;
    if (t1 < t2){
      ans += t2 - t1;
    } else {
      ans += t2 - t1 + 1440;
    }
  }
  cout << ans << endl;
}