#include <bits/stdc++.h>

using namespace std;

int f(string s) {
  string h = "", m = "";
  int l = 0;
  while (s[l] != ':') h += s[l++];
  l++;
  while (l < s.size()) m += s[l++];
  return atoi(h.c_str()) * 60 + atoi(m.c_str());
}

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

  int ans = 0;
  for (int i = 0; i < n; i++) {
    string s, t;
    cin >> s >> t;
    
    int ss = f(s), tt = f(t);
    ans += (ss > tt ? tt + 24 * 60 - ss : tt - ss);
  }

  cout << ans << endl;

  return 0;
}