P5682 [CSP-J2019 江西] 次大值

 

#include<cstdio>
#include<iostream>
#include<algorithm>
//#include<queue>
//#include<vector>
//#include<bits/stdc++.h>
#define ll long long
#define ddd printf("-----------------------\n");
using namespace std;
const int maxn=2e5+10 ;

int a[maxn],n;

int main()
{
    ios::sync_with_stdio(false);
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    sort(a+1,a+1+n); n=unique(a+1,a+1+n)-(a+1);
    
    if(n<=1){
        cout<<"-1\n";
        return 0;
    }
    cout<<max(a[n-2],a[n]%a[n-1])<<'\n';
    
    return 0;
}