#include <bits/stdc++.h>
using namespace std;
#define REP(a,b) for(long long a = 0;a < b;++a)
int main(){
	int n;
	cin >> n;
	vector<double> wow;
	REP(i,n){
		double tmp;
		cin >> tmp;
		wow.push_back(tmp);
	}
	double ans = 0;
	sort(wow.begin(),wow.end(),greater<double>());
	for(int i = 0;i < wow.size()-1;++i){
		for(int q = i+1;q < wow.size();++q){
			double puu = 0;
			for(int j = 0;j < wow.size();++j){
				if(j != i&&j != q){
					if(puu != 0){
						puu += wow[j];
						break;
					}
					puu += wow[j];
				}
			}
			ans = max(ans,puu / abs(wow[i]-wow[q]));
		}
	}
	cout << fixed << setprecision(20) << ans << endl;
	return 0;
}
