#include <stdio.h>
long int K;
unsigned int N;
long int L[10000000];
int main(){
	scanf("%d",&N);
	for(int i=0;i<N;i++){
		scanf("%d",&L[i]);
	}
	scanf("%d",&K);
	solve();
}
int C(double x){
	int num = 0;
	for(int i=0;i<N;i++){
		num += (int)(L[i] / x );
	}
	if(num >= K){
		return 1;
	}else{
		return 0;
	}
}

void solve() {
	double lb =0.0;
	double ub = 1000.0;
	double k = 2.0;
	double mid;
	for(int i =0; i<10000; i++){
		mid = (lb+ub)/k;
		if(C(mid) == 1){
			lb = mid;
		}else{
			ub = mid;
		}
	}
	printf("%1.15f\n",lb);
}