#include<cstdio>

 #include<cstring>

 #include<iostream>

 #include<algorithm>

 #include<cmath>

 using namespace std;

 #define dbg(x) cout<<#x<<" = "<<x<<endl

 const int maxn=,maxsize=;

 int n,ans=;

 int s[maxn],a[maxsize],siz=;

 int main(){

     scanf("%d",&n);

     for(int i=;i<=n;i++)  scanf("%d",&s[i]);

     for(int i=;i<n;i++)

         for(int j=i+;j<=n;j++){

             a[abs(s[i]-s[j])]=;

             siz=max(siz,abs(s[i]-s[j]));

         }

 //    dbg(siz);

     for(int i=;i<siz;i++){

         if(a[i])  continue;

         bool flag=;

         for(int p=(i<<);p<=siz;p+=i)

             if(a[p]){  flag=;  break;  }

         if(!flag){  ans=i;  break;  }

     }

     if(ans==)  ans=siz+;

     printf("%d\n",ans);

     return ;

 }