#include<stdio.h>
int main()
{
	int n;
	scanf("%d", &n);
	int i;
	int H, M, h, m;
	int ans = 0;
	for (i = 0; i < n; i++)
	{
		scanf("%d:%d %d:%d", &H, &M, &h, &m);
		M += 60 * H;
		m += 60 * h;
		if (M > m)
			m += 24 * 60;
		ans += m - M;
	}
	printf("%d\n", ans);
	return 0;
}