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

int main() {
	int n,h1,h2,m1,m2,sum=0;
	
	cin>>n;
	for(int i=0;i<n;++i){
		scanf("%d:%d",&h1,&m1);
		scanf("%d:%d",&h2,&m2);
		
		if(h1 > h2 || (h1 == h2 && m1 > m2)){
			sum += (h2 + 24 - h1) * 60 + (m2 - m1);
		}else{
			sum += (h2 - h1) * 60 + (m2 - m1);
		}
	}
	cout << sum << endl;
	return 0;
}