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

signed main(){
  int N; cin >> N;
  int ans = 0;
  for( int i = 0; i < N; ++i ){
    int H, M, h, m;
    scanf( "%d:%d", &H, &M );
    scanf( "%d:%d", &h, &m );
    int x = H * 60 + M;
    int y = h * 60 + m;
    int d = ( ( y - x ) % ( 60 * 24 ) + ( 60 * 24 ) ) % ( 60 * 24 );
    ans += d;
  }
  cout << ans << endl;
  return 0;
}