#include <bits/stdc++.h>
using namespace std;

int main()
{
	int N;
	cin >> N;
	cin.ignore( numeric_limits<streamsize>::max(), '\n' );
	int ans = 0;
	for( int i = 0; i < N; i++ ) {
		string buf;
		getline( cin, buf );
		int H, M, h, m;
		sscanf( buf.c_str(), "%d:%d %d:%d", &H, &M, &h, &m );
		if( h < H || h == H && m < M ) h += 24;
		int st = H * 60 + M;
		int end = h * 60 + m;
		ans += end - st;
	}

	cout << ans << endl;
}