#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n, a[N], b[N], flag = 1;
int main() {
	int t = 0;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	sort(a + 1, a + 1 + n);
	for (int i = 1; i <= n; i++) {
		if (a[i] != b[t]) {
			t++;
			b[t] = a[i];
		}
	}
	if (t <= 2) {
		cout << "-1";
		return 0;
	} else {
		cout << max(b[t - 2], b[t] % b[t - 1]);
	}
}

P5682 [CSP-J2019 江西] 次大值

求助