#include <iostream>

using namespace std;

int main()
{
	int N, h, m, sl, wk, ans = 0;
	cin >> N;
	for (int i = 0; i < N; i++) {
		scanf("%d:%d", &h, &m);
		sl = h * 60 + m;
		scanf("%d:%d", &h, &m);
		wk = h * 60 + m;
		ans += (sl < wk ? wk - sl : wk + 1440 - sl);
	}
	cout << ans << endl;
	return 0;
}