#include <iostream>
#include <string>
using namespace std;

int main()
{
	int N, sum = 0;
	string HM, hm;
	cin >> N;
	for(int i = 0; i < N; ++i)
	{
		cin >> HM >> hm;
		sum += (((24 * 60)
			+ (stoi(hm.substr(0, hm.find(':'))) * 60 + stoi(hm.substr(hm.find(':') + 1, hm.length() - hm.find(':') - 1))
				- (stoi(HM.substr(0, HM.find(':'))) * 60 + stoi(HM.substr(HM.find(':') + 1, HM.length() - HM.find(':') - 1)))))
			% (24 * 60));
	}

	cout << sum << endl;
	return 0;
}