#include<bits/stdc++.h>
using namespace std;
int n,Ts,T[100005],i,j,k,h,m,s;
int const g=12*60*60;
int main()
{
	scanf("%d",&n);
	scanf("%d%d%d",&h,&m,&s);
	h%=12;
	Ts=h*60*60+m*60+s;
	for(i=1;i<=n;i++)
	{
		scanf("%d%d%d",&h,&m,&s);
		h%=12;
		T[i]=h*60*60+m*60+s;
		T[i]-=Ts;
		if(T[i]<0) T[i]+=g;
	}
	sort(T+1,T+n+1);
	int ans=T[n];
	for(i=2;i<=n;i++) ans=min(ans,(g-T[i])*2+T[i-1]);
//	ans=min(ans,g-T[1]*2);
	ans=min(ans,g-T[1]);
	for(i=1;i<n;i++) ans=min(ans,T[i]*2+(g-T[i+1]));
	ans*=6;
	printf("%d.00\n",ans);
	return 0;
}