// yukicoder: No.67 よくある棒を切る問題 (1)
// bal4u 2019.9.7

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

typedef long long ll;

//// 高速入力
#if 1
int getchar_unlocked(void);
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

ll inLL() {
	ll n = 0; int c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

int L[200005];

int main()
{
	int i, loop, N; ll K, s; double l, r, m;

	N = in(); 
	s = 0; for (i = 0; i < N; i++) L[i] = in(), s += L[i];
	K = inLL();
	l = 0; r = (double)s/K+1;
	loop = 50; while (loop--) {
      m = (l + r) / 2.0;
	  s = 0; for (i = 0; i < N; i++) s += (ll)((L[i])/m);
	  if (s < K) r = m; else l = m;
    }
	printf("%.12lf\n", m);
	return 0;
}