#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

const int N = 2e5 + 5;

int n, a[N];

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++) scanf("%d", a + i);
	sort(a + 1, a + 1 + n);
	int ans = 0;
	for (int u = 1; u <= n; u++) {
		for (int v = u + 1; v <= min(n, u + 20); v++) {
			for (int w = v + 1; w <= min(n, v + 20); w++) {
				ans = max(ans, (a[u] + a[v]) % a[w]);
				ans = max(ans, (a[w] + a[u]) % a[v]);
				ans = max(ans, (a[v] + a[w]) % a[u]);
			}
		}
	}
	printf("%d\n", ans);
}