#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
typedef long long ll;

int N, L[200010];
ll K;
bool func(double x)
{
    ll cnt=0;
    for(int i=0;i<N;++i)
        cnt+=(ll)(L[i]/x);
    return cnt>=K;
}
int main()
{
    while (cin>>N) {
        for(int i=0;i<N;++i) cin>>L[i];
        cin>>K;
        double lb=0, ub=1e11;
        for(int $=0;$<100;++$) {
            double x=(ub+lb)*0.5;
            if (func(x))
                lb=x;
            else
                ub=x;
        }
        printf("%.10f\n", lb);
    }
}