//inlclude前用define 
#define _USE_MATH_DEFINES

//include
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<cmath>

using namespace std;
//typedef
typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<char> VC;

int main() {
	int n;
	cin >> n;
	VI h1(n), m1(n), h2(n), m2(n);
	char a, b;
	for (int i = 0; i < n; i++) {
		cin >> h1[i] >>a>> m1[i] >> h2[i] >>b>> m2[i];
	}
	int sum = 0;
	for (int i = 0; i < n; i++) {
		if (h1[i] > h2[i]) {
			h2[i] += 24;
		}
		sum += (h2[i] - h1[i]) * 60;
		sum += (m2[i] - m1[i]);
	}
	cout << sum << endl;
	return 0;
}