#include<bits/stdc++.h>
using namespace std;
#define maxn 1000100
int n,i,a[5500],j,ans,t;bool b[maxn];
int main()
{
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
    i=n-1;
    while (ans==0)
    {
        t=0;
        for(j=0;j<=i;j++)
            b[j]=false;
        for(j=1;j<=n;j++)
        {
            if(b[a[j]%i]==true)    {i++,t+=1;}
            if(t==1) break;
            b[a[j]%i]=true;
        }    
        if (t==0) ans=i;
    }    
    printf("%d",ans);
    return 0;
}