#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<cstring>

#include<string>

#include<cmath>

#include<map>

#include<set>

#include<vector>

#include<algorithm>

#include<stack>

#include<queue>

#include<cctype>

#include<sstream>

using namespace std;

#define pii pair<int,int>

#define LL long long int

const int eps=1e-;

const int INF=;

const int maxn=;

int n,a[maxn],ans=-;

int main()

{

    //freopen("in9.txt","r",stdin);

    //freopen("out.txt","w",stdout);

    scanf("%d",&n);

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

    {

        scanf("%d",&a[i]);

    }

    if(n==){printf("0\n");return ;}

    sort(a,a+n);

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

    {

        if(i&&a[i]==a[i-]) continue;

        for(int t=a[i]*;t<=a[n-];t+=a[i])

        {

            int p=lower_bound(a,a+n,t)-a;

            ans=max(ans,a[p-]%a[i]);

        }

        ans=max(ans,a[n-]%a[i]);

    }

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

    //fclose(stdin);

    //fclose(stdout);

    return ;

}