#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(void) {
	int n;
	cin >> n;
	string HM, hm;
	int ans = 0;
	for (int i = 0; i < n; ++i) {
		cin >> HM >> hm;
		int pos = HM.find(':');
		string H = HM.substr(0, pos),
			M = HM.substr(pos + 1);

		pos = hm.find(':');
		string h = hm.substr(0, pos),
			m = hm.substr(pos + 1);

		int h1 = stoi(H), m1 = stoi(M),
			h2 = stoi(h), m2 = stoi(m);
		if (h1 == h2) {
			if (m2 >= m1) ans += m2 - m1;
			else ans += 1440 - (m1 - m2);
		}
		else if (h2 > h1) {
			ans += 60 - m1;
			ans += (h2 - h1 - 1) * 60;
			ans += m2;
		}
		else if (h1 > h2) {
			ans += 60 - m1;
			ans += (24 - h1 - 1) * 60;
			ans += h2 * 60;
			ans += m2;
		}
	}
	cout << ans << endl;
	return 0;
}