import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

int readint() {
    return readln.chomp.to!int;
}

int[] readints() {
    return readln.split.map!(to!int).array;
}

bool can(double len, long k, long[] ls) {
    long n = 0;
    foreach (x; ls) {
        n += x / len;
    }
    return n >= k;
}

double calc(long k, long[] ls) {
    double ans = 0;
    double lo = 0;
    double hi = 10 ^^ 9;
    foreach (_; 0 .. 100) {
        auto m = (lo + hi) / 2;
        if (can(m, k, ls)) {
            ans = max(ans, m);
            lo = m;
        }
        else {
            hi = m;
        }
    }
    return ans;
}

void main() {
    readln;
    auto ls = readln.split.map!(to!long).array;
    long k = readln.chomp.to!long;

    auto ans = calc(k, ls);
    writefln("%.9f", ans);
}