#include <stdio.h>

int main() {
	int n, hs, ms, he, me, ts, te, sum = 0, i;

	scanf("%d", &n);
	for (i = 0; i < n; i++) {
		scanf("%d:%d %d:%d", &hs, &ms, &he, &me);
		ts = hs * 60 + ms;
		te = he * 60 + me;
		if (ts > te) sum += 24 * 60 - (ts - te);
		else sum += te - ts;
	}

	printf("%d\n", sum);
	return 0;
}