代码如下

#include<bits/stdc++.h>
using namespace std;

int n;
long long a[200000],tong[20000000],ans=0;

int main(){
    //freopen("submaximum.in","r",stdin);
    //freopen("submaximum.out","w",stdout);
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(a[i]==a[j]){
                continue;
            }
            tong[a[i]%a[j]]=1;
            tong[a[j]%a[i]]=1;
        }
    }
    for(int i=20000000;i>=1;i--){
        if(tong[i]==1){
            //cout<<i<<endl;
            ans++;
        }
        if(tong[i]==1 && ans==2){
            cout<<i<<endl;
        }
        //cout<<ans<<endl;
    }
    if(ans<2){
        cout<<"-1";
    }
    return 0;
}