#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
const int INF=0x3f3f3f3f;
int n,a[N];
void Accepted( int x , int a[] , int & len )//Accepted()
{
    len = 0;
    while ( x != 0 )
	{
        a[++len] = x % 7;
        x /= 7;
    }
}
int WrongAnswer(int x,int y){
	int a[7],b[7],c[7],len1,len2,len;
    memset(a,0,sizeof(a));
    memset(b,0,sizeof(b));
    memset(c,0,sizeof(c));
    Accepted(x,a,len1);
    Accepted(y,b,len2);
    len=max(len1,len2);
    for(int i=1;i<=len;i++){
        if(a[i]!=b[i])c[i]=1;
    }
    int n=0;
    for(int i=len;i>=1;i--){
        n=n*2+c[i];
    }
    return n;
}
int main()
{
	int end;
	cin >> n;
	for(int i=1;i<=n;i++)
	{
		cin >> a[i];
	}
	for(int i=1;i<n;i++){
        for(int j=i+1;j<=n;j++){
            int v=WrongAnswer(a[i],a[j]);
            if(abs(v-123)<abs(end-123)){
                end=v;
            }
            if(end==v&&v<end){
                end=v;
            }
        }
    }
    cout<<end;
	return 0;
}
//老登布置的作业系列

it so long