#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n; cin >> n;
  int sum = 0;
  REP (i, n) {
    int h1, m1, h2, m2;
    scanf(" %d:%d %d:%d", &h1, &m1, &h2, &m2);
    cerr << h1 << " " << m1 << " " << h2 << " " << m2 << endl;
    int t1 = 60 * h1 + m1;
    int t2 = 60 * h2 + m2;
    int d = t2 - t1;
    if (d < 0)
      d += 60 * 24;
    sum += d;
  }
  cout << sum << endl;
  
  return 0;
}