#include<iostream>
#include<stdio.h>
using namespace std;

int main(void)
{
	int i, n, h1, m1, h2, m2,ans=0;

	cin >> n;

	for (i = 0; i < n; i++) {
		scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
		ans += (h2 - h1) * 60 + (m2 - m1);
		if (h1 > h2)ans += 1440;
	}
	cout << ans << endl;


	return 0;
}