#include <iostream>

using namespace std;

int main(int argc, const char* argv[])
{
	int N;
	cin >> N;
	int sum = 0;
	for (int i = 0; i < N; i++) {
		int H, M, h, m;
		scanf("%d:%d %d:%d", &H, &M, &h, &m);
		if (H < h || H == h && M < m) {
		}
		else {
			sum += 24 * 60;
		}
		sum += (h - H) * 60 + (m - M);
	}
	cout << sum << endl;
	return 0;
}