#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int main(void) {
	int num, i, hs, he, ms, me;
	int sum = 0;

	scanf("%d", &num);

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

	printf("%d\n", sum - (num * 60));

	return 0;
}