#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 intconst int eps=1e-8;const int INF=1000000000;const int maxn=200009;int n,a[maxn],ans=-1;int main(){    //freopen("in9.txt","r",stdin);    //freopen("out.txt","w",stdout);    scanf("%d",&n);    for(int i=0;i<n;i++)    {        scanf("%d",&a[i]);    }    if(n==1){printf("0\n");return 0;}    sort(a,a+n);    for(int i=0;i<n-1;i++)    {        if(i&&a[i]==a[i-1]) continue;        for(int t=a[i]*2;t<=a[n-1];t+=a[i])        {            int p=lower_bound(a,a+n,t)-a;            ans=max(ans,a[p-1]%a[i]);        }        ans=max(ans,a[n-1]%a[i]);    }    printf("%d\n",ans);    //fclose(stdin);    //fclose(stdout);    return 0;}