#include <bits/stdc++.h>

#ifndef LOCAL_
#define fprintf if( false ) fprintf
#endif // LOCAL_
#define dumpi(x1) fprintf(stderr, "#%s.%d (%s) = (%d)\n", __func__, __LINE__, #x1, x1);
#define dumpl(x1) fprintf(stderr, "#%s.%d (%s) = (%ld)\n", __func__, __LINE__, #x1, x1);
#define dumpd(x1) fprintf(stderr, "#%s.%d (%s) = (%lf)\n", __func__, __LINE__, #x1, x1);

long n;
long xs[212345];
long k;

bool check(double x) {
  if( x == 0 ) return false;
  long res = 0;
  for(int i = 0; i < n; ++i) {
    res += (xs[i] / x + 1e-10);
  }
  dumpl(res);
  return k <= res;
}

int main() {
  scanf("%ld", &n);
  for(int i = 0; i < n; ++i) {
    scanf("%ld", &xs[i]);
  }
  scanf("%ld", &k);
  double z = 0;
  double diff = (1LL << 40);
  for(int i = 120; i >= 0; --i) {
    double nz = z + diff;
    diff /= 2;
    dumpd(nz);
    if( check(nz) ) {
      z = nz;
      continue;
    }
  }
  printf("%.20lf\n", z);

  return 0;
}