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

int main(){
	int n;
	cin >> n;
	char zz;
	int a,b,c,d;
	int time = 0;
	for(int i = 0; i < n; i++){
		cin >> a >> zz >> b >> c >> zz >> d;
		while(a != c){
			if(a == 23) {
				time += 60 - b;
				a = b = 0;
			}else{
				time += 60;
				a++;
			}
			if(a == c) time += d - b;
		}
	}
	cout << time << endl;
	return 0;
}