#include <bits/stdc++.h>
#define rep(i, a, n) for (int i = a; i < n; i++)
#define repr(i, a, n) for (int i = n - 1; i >= a; i--)
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chmax(T &a, T b) { a = max(a, b); }

int time_convert(string d) {
  int sp = d.find(':');
  int one = stoi(d.substr(0, sp));
  int two = stoi(d.substr(sp + 1, d.size() - (sp + 1)));
  return one * 60 + two;
}

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

  int n;
  cin >> n;
  int ans = 0;
  rep(i, 0, n) {
    string a, b;
    cin >> a >> b;
    int start = time_convert(a);
    int end = time_convert(b);
    if (start > end)
      ans += end + (1440 - start);
    else
      ans += end - start;
  }
  cout << ans << endl;
}