#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int main(){
  int n;
  cin >> n;

  double m[n],sa;
  for(int i = 0;i < n;i++) cin >> m[i];
  sort(m,m+n);
  sa = m[1] - m[0];
  
  for(int i = 2;i <=n-3;i++){
    if(sa > m[i]-m[i-1]) sa = m[i] - m[i-1];
  }

  double ans1 = (m[n-1]+m[n-2])/sa;
  double ans2 = (m[n-1]+m[n-4])/(m[n-3]-m[n-2]);
  double ans3 = (m[n-3]+m[n-4])/(m[n-1]-m[n-2]);
  

  if(ans1 >= ans2 && ans1 >= ans3) printf("%.6f\n",ans1);
  else if(ans2 >= ans3) printf("%.6f\n",ans2);
  else printf("%.6f\n",ans3);
  return (0);
}