#include<iostream>
#include<cstdio>
using namespace std;
int main() {
	int n;cin>>n;
	int a,b,c,d,sum=0;
	for(int i=0;i<n;i++)
	{
		scanf("%d:%d %d:%d",&a,&b,&c,&d);
		b+=a*60;
		d+=c*60;
		d-=b;
		if(d<0)d+=1440;
		sum+=d;
	}
	cout<<sum<<endl;
}