#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

int main() {
  int N;
  cin >> N;
  int ts, te, hs, he, ms, me, ans = 0;
  rep(i, 0, N) {
    scanf("%d:%d %d:%d", &hs, &ms, &he, &me);
    ts = hs * 60 + ms;
    te = he * 60 + ms;
    if (ts > te) te += 24 * 60;
    ans += te - ts;
  }
  cout << ans << endl;
  getchar();
}