#include <iostream>
using namespace std;

int main()
{
	int ans = 0;
	int N;
	scanf("%d", &N);

	for (int i = 0; i < N; i++)
	{
		int H, M, h, m;
		scanf("%d:%d %d:%d", &H, &M, &h, &m);

		int mini_ans = (h - H + 24) * 60 + m - M;
		mini_ans %= 24 * 60;
		ans += mini_ans;
	}
	cout << ans << endl;
}