#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
#define mid ((l+r)/2)
using namespace std;
const int maxn=50+10;
int n,d[maxn];
bool cmp(int a,int b){
	return a>b;
}
int cal(int a,int b){
	return ((a-b)%24+24)%24;
}
bool check(int c){
	int a[maxn]={0},last=d[1];
	for(int i=1;i<=n;i++)
		a[i]=d[i];
	for(int i=2;i<=n;i++)
		if(last-a[i]<c)a[i]*=-1;
		else last=a[i];
	for(int i=0;i<=n;i++)
		for(int j=0;j<=n;j++)
			if(i!=j && min(cal(a[i],a[j]),cal(a[j],a[i]))<c)
	return false;
	return true;
}
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
		scanf("%d",&d[i]);
	sort(d+1,d+n+1,cmp);
	int l=0,r=12;
	while(l+1<r){
		if(check(mid))l=mid;
		else r=mid-1;
	}
	if(check(r))printf("%d\n",r);
	else printf("%d\n",l);
	return 0;
}