#include <iostream>
#include <iomanip>
#include <vector>

typedef long long ll;

int main(void)
{
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(8);
  int n;
  std::cin >> n;
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    int ha, hb, ma, mb;
    char c;
    std::cin >> ha >> c >> ma >> hb >> c >> mb;
    int a = ha * 60 + ma, b = hb * 60 + mb;
    if (a > b) b += 24 * 60;
    ans += b - a;
  }
  std::cout << ans << std::endl;
  return 0;
}