#include <stdio.h>

int main(void) {
	int i, N, H[31], M[31], h[31], m[31];
	int s, e, t, total = 0;
	scanf("%d", &N);
	for(i = 1;i <= N;i++){
		scanf("%d:%d%d:%d", &H[i], &M[i], &h[i], &m[i]);
	}
	for(i = 1;i <= N;i++){
		s = H[i] * 60 + M[i];
		e = h[i] * 60 + m[i];
		if(s > e)t = 24 * 60 - s + e;
		else     t = e - s;
		total += t;
	}
	printf("%d\n", total);

	return 0;
}