#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <iomanip>
#include <cmath>
using namespace std;
#define diff(x,y) ((x > y) ? (x - y) : (y - x))
#define us(x) (x > 0) ? x : x * -1

int main(){
	char sute;
	int n, A, Ah, Am, B, Bh, Bm, ans = 0;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> Ah >> sute >> Am >> Bh >> sute >> Bm;
		A = Ah * 60 + Am;
		B = Bh * 60 + Bm;
		if (A > B)	B += 24 * 60;
		ans += B - A;
	}
	cout << ans << endl;
	return 0;
}