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


int main(){
  int N,ans=0;
  cin >> N;
  for(int i=0;i<N;i++){
    int a,b,c,d;
    char e,f;
    cin >> a >> e >> b >> c >> f >> d;
    int A = a*60+b;
    int B = c*60+d;
    B += 1440;
    int C = B-A;
    C %= 1440;
    ans += C;
  }
  cout << ans << endl;
}