#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>

using namespace std;

int main()
{	
	int n;
	cin>>n;

	long res=0;
	for(int i=0;i<n;i++){
		int H,h,M,m;
		scanf("%d:%d",&H,&M);
		scanf("%d:%d",&h,&m);

		long t1=H*60+M,t2=h*60+m;
		if(t1>t2) t2+=24*60;

		res+=t2-t1;

	}
	cout<<res<<endl;

	return 0;

}