#include <bits/stdc++.h>
using namespace std;
const int N=1e5+7;
const int maxrun=1145;
int n;
int a[N],vis[N];
int main(){
	freopen("arrayy.in","r",stdin);
	freopen("arrayy.out","w",stdout);	
	srand(time(0));
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	int t=maxrun;
	int maxx=-1e9;
	while(t--){
		random_shuffle(a+1,a+n+1);
		int ans=a[1];
		for(int i=2;i<=n;i++){
			ans=ans%a[i];
		}
		maxx=max(maxx,ans);
	}
	cout<<maxx; 
	
	
	return 0;
}