#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<iomanip>
using namespace std;
typedef long long int lont;
int main() {
	int N;
	cin >> N;
	int h1, m1, h2, m2;
	char c1, c2;
	int sum = 0;
	for (int ia = 0; ia < N; ia++) {
		cin >> h1 >> c1 >> m1 >> h2 >> c2 >> m2;
		if ((h1 < h2) || (h1 == h2 && m1 <= m2)) {
			sum += (h2 * 60 + m2) - (h1 * 60 + m1);
		}
		else {
			sum += 1440 - 60 * (h1 - h2) - (m1 - m2);
		}
	}
	cout << sum << endl;
}