#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  int ans = 0;
  rep(i, n) {
    int a, b, c, d;
    scanf("%d:%d %d:%d", &a, &b, &c, &d);
    int dif = (c * 60 + d) - (a * 60 + b);
    if (dif < 0) dif += 24 * 60;
    ans += dif;
  }
  cout << ans << endl;
  return 0;
}