#include <bits/stdc++.h>

using namespace std;

const int mod = 24 * 60;

int main() {
	int N; cin >> N;
	int ans = 0;
	for (int i = 0; i < N; ++i) {
		int h1, m1, h2, m2;
		scanf("%d:%d%d:%d", &h1, &m1, &h2, &m2);
		int t1 = h1*60+m1;
		int t2 = h2*60+m2+mod;
		ans += (t2-t1)%mod;
	}
	cout << ans << endl;
}