#include<iostream>
using namespace std;
int main(void){
	int sum = 0, n; cin >> n;
	for (int i = 0; i < n; i++)
	{
		int H, M, h, m; char c;
		cin >> H >> c >> M >> h >> c >> m;
		sum += (((h * 60 + m) - (H * 60 + M)) + 1440) % 1440;
	}
	cout << sum << endl;
	return 0;
}