#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define sz(n) (int)(n).size()
using namespace std;

int main() {
	int n;
	char c;
	cin >> n;
	int ans = 0;
	REP(i, n) {
		int h1, m1, h2, m2;
		cin >> h1 >> c >> m1 >> h2 >> c >> m2;
		ans += ((h2 * 60 + m2) - (h1 * 60 + m1) + 24 * 60) % (24 * 60);
	}
	cout << ans << endl;
	return 0;
}