#include <bits/stdc++.h>
using namespace std;
#define ld long double
const int N = 1e5 + 1;
int n, c, a[N];
ld foo() {
  int sum = 0, maxn = 0;
  for (int i = 1; i <= n; i++)
    sum += a[i], maxn = max(maxn, a[i]);
  return 1. * sum / maxn;
}
ld bar() {
  ld out = 0, sum = 0;
  for (int i = 1; i <= n; i++)
    sum += a[i], out += sqrtl(a[i]);
  return out * out / sum;
}
int main() {
  scanf("%d%d", &n, &c);
  for (int i = 1; i <= n; i++)
    scanf("%d", a + i);
  ld ans1 = foo(), ans2 = bar();
  printf("%.10Lf", (ans1 * c + ans2 * (100 - c) )/ 100);
  return 0;
}