#include <stdio.h>
#include <algorithm>
#include <deque>
using namespace std;
using ll = long long;

//70
int main() {
	int n, h[2], m[2], time[2], slept, total = 0;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		scanf("%d:%d %d:%d", h, m, h + 1, m + 1);
		time[0] = h[0] * 60 + m[0];
		time[1] = h[1] * 60 + m[1];
		slept = time[1] - time[0];
		if (slept < 0)
			slept = slept + 24 * 60;
		total += slept;
	}
	printf("%d\n", total);
}