#include<bits/stdc++.h>
using namespace std;
const int S=1e7;
int s,t,l,a[S],b[S]; 
int main(){
	cin>>s;
	for(int i=1;i<=s;i++){
		cin>>a[i];
	}
	for(int i=1;i<=s;i++){
		for(int j=1;j<=s;j++){
			if(i!=j){
				++l;
				//b[l]=a[i]%a[j];	
			}
		}
	} 
	sort(b+1,b+l+1);
	unique(b+1,b+l+1);
	l=unique(b+1,b+l+1)-b-1;	
	if(l<2){cout<<"-1";return 0;}
	int first=-1e8,second=-1e8;
	for(int i=1;i<=l;i++){
		first=max(first,b[i]);
	}
	for(int i=1;i<=l;i++){
		b[i]-=first;
	}
	for(int i=1;i<=l;i++){
		if(b[i]!=0) second=max(second,b[i]);
	}
	cout<<first+second;
}

Runtime Error.
Received signal 8: Floating-point exception.