C++ :

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

int main()
{
	double a[110];
	int n;
	double X;
	//freopen("bet.in","r",stdin);
	//freopen("bet.out","w",stdout);
	while(scanf("%d",&n) != EOF) {
		for(int i = 1; i <= n; i ++)
			scanf("%lf",&a[i]);
		scanf("%lf",&X);

		double lt = 0,rt = 1000000, mid, ans = 0;
		double eps = 1e-8;
		while(lt + eps <= rt) {
			mid = (lt + rt) / 2;
			double sum = 0;
			for(int i = 1; i <= n; i ++) {
				sum += mid / a[i];
			}
			if(sum <= X) {
				ans = mid;
				lt = mid + eps;
			}
			else rt = mid - eps;
		}

		printf("%.2lf\n",ans);
	}
	return 0;
}