#include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 using namespace std;

 const int maxn =  + ;

 const int maxm =  + ;

 int a[maxn], f[maxm];

 int main()

 {

     int n; scanf("%d", &n);

     for(int i = ; i < n; i++) scanf("%d", a + i);

     sort(a, a + n);

     n = unique(a, a + n) - a;

     int M = a[n-];

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

         for(int j = a[i] + ; j <= a[i+]; j++) f[j] = a[i];

     int ans = ;

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

     {

         for(int j = a[i] * ; j <= M; j += a[i])

         {

             ans = max(ans, f[j] % a[i]);

         }

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

     }

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

     return ;

 }