#include<stdio.h>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;

int main() {

	int N, H, M, h, m;
	cin >> N;
	long long sum = 0;
	for (int i = 0; i < N; i++) {
		scanf("%d:%d %d:%d" ,&H, &M, &h, &m);

		if (H <= h) {
			sum -= (60*H + M);
		}
		else {
			sum += (60 * (23 - H) + (60 - M));
		}

		sum += (60 * h + m);
	}

	cout << sum << endl;

	return 0;
}