/* -*- coding: utf-8 -*-
 *
 * 70.cc: No.70 睡眠の重要性! - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

int hm2min(string &hm) {
  int h = 0, m = 0, pos = 0;
  while (pos < hm.size() && hm[pos] != ':')
    h = h * 10 + hm[pos++] - '0';
  pos++;
  while (pos < hm.size())
    m = m * 10 + hm[pos++] - '0';
  return h * 60 + m;
}

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;

  int sum = 0;
  for (int i = 0; i < n; i++) {
    string hm0, hm1;
    cin >> hm0 >> hm1;
    int m0 = hm2min(hm0);
    int m1 = hm2min(hm1);

    int mm = m1 - m0;
    if (mm < 0) mm += 24 * 60;
    sum += mm;
  }

  printf("%d\n", sum);
  return 0;
}