#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  cin >> N;
  vector<int> H(N), M(N), h(N), m(N);
  char c;
  for (int i = 0; i < N; ++i) {
    cin >> H[i] >> c >> M[i] >> h[i] >> c >> m[i];
  }

  for (int i = 0; i < N; ++i) {
    M[i] += H[i] * 60, m[i] += h[i] * 60;
    if (M[i] > m[i]) {
      m[i] += 24 * 60;
    }
  }

  int ans = 0;
  for (int i = 0; i < N; ++i) {
    ans += m[i] - M[i];
  }

  cout << ans << endl;
}