#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n, h1, m1, h2, m2;
	int total = 0;

	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
		int t2 = h2 * 60 + m2;
		int t1 = h1 * 60 + m1;

		if (t2 < t1) {
			total += 60 * 24 + t2 - t1;
		} else {
			total += t2 - t1;
		}
	}
	cout << total << endl;
	return 0;
}