import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop, core.thread;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) throw new EOFException; tokens = readln.split; } auto token = tokens[0]; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


int N;
real[] L;
long K;

void main() {
  try {
    for (; ; ) {
      N = readInt();
      L = new real[N];
      foreach (i; 0 .. N) {
        L[i] = readReal();
      }
      K = readLong();
      
      real lo = 0.0, hi = L.maxElement;
      foreach (_; 0 .. 70) {
        const mid = (lo + hi) / 2.0;
        long sum;
        foreach (i; 0 .. N) {
          sum += cast(long)(floor(L[i] / mid));
        }
        ((sum >= K) ? lo : hi) = mid;
      }
      writefln("%.10f", lo);
    }
  } catch (EOFException e) {
  }
}