#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define INF 1000000010
#define EPS 1e-9
#define fst first
#define scd second

#define debug(x) cout<<x<<endl;
#define repi(i,x,n) for(int i=x;i<n;i++)
#define rep(i,n) repi(i,0,n)
#define lp(i,n) repi(i,0,n)
#define repn(i,n) for(int i=n;i>=0;i--)
#define int long long
#define endl "\n"


signed main(){
  cin.tie(0);	
  ios::sync_with_stdio(false);
  cout<<fixed<<setprecision(12);
  int n;
  cin>>n;
  int a[1000];
  rep(i,n) cin>>a[i];
  sort(a,a+n);
  double ans=0;
  rep(i,n-2){
    ans=max((double)(a[n-1]+a[n-2])/(double)(a[i+1]-a[i]),ans);
  }
  ans=max((double)(a[n-3]+a[n-4])/(double)(a[n-1]-a[n-2]),ans);
  ans=max((double)(a[n-1]+a[n-4])/(double)(a[n-2]-a[n-3]),ans);
  cout<<ans<<endl;

  return 0;
}

