#include <bits/stdc++.h>
using namespace std;
template <class T>
T gcd(T a, T b) {
  return (b != 0 ? gcd<T>(b, a % b) : a);
}
template <class T>
T lcm(T a, T b) {
  return (a / gcd<T>(a, b) * b);
}
template <class T>
inline bool read(T &x) {
  int c = getchar();
  int sgn = 1;
  while (~c && c < '0' || c > '9') {
    if (c == '-') sgn = -1;
    c = getchar();
  }
  for (x = 0; ~c && '0' <= c && c <= '9'; c = getchar()) x = x * 10 + c - '0';
  x *= sgn;
  return ~c;
}
const int INF = 2000000009;
const int MX = 1000001;
const double EPS = 1e-9;
const int MOD = 1000000007;
int cnt[MX];
int main() {
  int n = ({
    int a;
    read(a);
    a;
  });
  int a[n];
  for (int i = 0; i < n; i++)
    cnt[a[i] = ({
          int a;
          read(a);
          a;
        })] = 1;
  int ans = 0;
  sort(a, a + n);
  for (int i = 2; i < MX; i++) {
    if (!cnt[i]) continue;
    int v = i;
    while (v < MX) {
      int ind = upper_bound(a, a + n, v + i - 1) - a - 1;
      ans = max(ans, a[ind] - v);
      v += i;
    }
  }
  printf("%d\n", ans);
  return 0;
}
