#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	vector<string> e(n), f(n);
	vector<int> a(n), b(n), c(n), d(n);
	for (int i = 0; i < n; i++) {
		cin >> e[i] >> f[i];
		if (e[i][1] == ':') {
			a[i] = e[i][0] - '0';
		}
		else {
			a[i] = (e[i][0] - '0')*10+ e[i][1] - '0';
		}
		if (e[i][e[i].length()-2] == ':') {
			b[i] = e[i][e[i].length() - 1] - '0';
		}
		else {
			b[i] = (e[i][e[i].length() - 2] - '0') * 10 + e[i][e[i].length() - 1] - '0';
		}
		if (f[i][1] == ':') {
			c[i] = f[i][0] - '0';
		}
		else {
			c[i] = (f[i][0] - '0') * 10 + f[i][1] - '0';
		}
		if (f[i][f[i].length() - 2] == ':') {
			d[i] = f[i][f[i].length() - 1] - '0';
		}
		else {
			d[i] = (f[i][f[i].length() - 2] - '0') * 10 + f[i][f[i].length() - 1] - '0';
		}
	}
	int g = 0;
	for (int i = 0; i < n; i++) {
		g += ((c[i] + 23 - a[i] )* 60 + d[i] + 60 - b[i])%1440;
	}
	cout << g << endl;
}