#include<stdio.h>
#include<stdlib.h>

typedef long long int ln;

void run(void){
  int n;
  scanf("%d",&n);
  int *len=(int *)malloc(sizeof(int)*n);
  ln sumLen=0;
  int maxLen=0;
  int i;
  for(i=0;i<n;i++){
    scanf("%d",len+i);
    sumLen+=len[i];
    maxLen=(maxLen<len[i]?len[i]:maxLen);
  }
  ln k;
  scanf("%lld",&k);

  double min=(double)maxLen/k;
  double max=(double)sumLen/k;
  double mid=(max+min)/2;
  do{
    ln count=0;
    for(i=0;i<n;i++){
      count+=(ln)(len[i]/mid);
    }
    if(count>=k){
      min=mid;
    } else {
      max=mid;
    }
    mid=(max+min)/2;
  }while(mid-min>=1e-9 && (mid-min)/min>=1e-9);

  printf("%.10lf\n",mid);
  return;
}

int main(void){
  run();
  return 0;
}