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

int main() {
	int N, H, M, GTB, GU, count = 0;
	char c;
	cin >> N;
	for (int i = 0; i < N; i++) {
		cin >> H >> c >> M;
		GTB = 60 * H + M;
		cin >> H >> c >> M;
		GU = 60 * H + M;
		count += (GU + 1440 - GTB) % 1440;
	}
	cout << count << endl;
}