#include <bits/stdc++.h>
using namespace std;

int main() {
	int N;
	cin >> N;

	int s = 0;
	for (int i = 0; i < N; i++) {
		int H, M, h, m;
		scanf("%d:%d %d:%d\n", &H, &M, &h, &m);
		//cout << H << ' ' << M << ' ' << h << ' ' << m << endl;

		int d = (h * 60 + m) + (24 * 60) - (H * 60 + M);
		d %= 24 * 60;
		s += d;
		//cout << d << endl;
	}

	cout << s << endl;
}