#include<iostream>
#include<cstdio>
#include<string>
#include<algorithm>
using namespace std;

int main() {
	int n, h, m, ht, mt;
	scanf("%d", &n);

	int ans = 0;
	for (int i = 0; i < n; i++)
	{
		scanf("%d:%d %d:%d", &h, &m, &ht, &mt);
		int a = h * 60 + m;
		int b = ht * 60 + mt;
		if (b > a)
		{
			ans += (b - a);
		}
		else
		{
			ans += (b + 1440 - a);
		}
	}
	cout << ans << endl;

	return 0;
}