#include <algorithm>
#include <iostream>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <list>
#include <cmath>
#include <stack>
#include <string>
#include <cstring>
#include <numeric>
#include <iomanip>
using namespace std;
//
const int inf=1e9+7;//0x3f
//
int main(){
	int N;
	int D[50];
	int cnt[13];
	fill(cnt,cnt+13,0);
	cin>>N;
	for(int i=0;i<N;i++){
		cin>>D[i];
		cnt[D[i]]++;
	}
	if(cnt[0]==1||cnt[12]==2){
		cout<<0<<endl;
		return 0;
	}else{
		for(int i=1;i<12;i++){
			if(cnt[i]>=3){
				cout<<0<<endl;
				return 0;
			}
		}
	}
	int ans=0;
	for(int i=0;i<(1<<11);i++){
		int diff=inf;
		vector<int> V;
		V.push_back(0);
		for(int j=0;j<11;j++){
			if(cnt[j+1]==0){
				continue;
			}else if(cnt[j+1]==1){
				if((i>>j)&1){
					V.push_back(j+1);
				}else{
					V.push_back(24-(j+1));
				}
			}else{
				V.push_back(j+1);
				V.push_back(24-(j+1));
			}
		}
		if(cnt[12]==1){
			V.push_back(12);
		}
		sort(V.begin(),V.end());
		for(int j=0;j<V.size()-1;j++){
			diff=min(diff,abs(V[j]-V[j+1]));
		}
		diff=min(diff,abs(24-V[V.size()-1]));
		ans=max(ans,diff);
	}
	cout<<ans<<endl;
	return 0;
}