#include<cmath>
#include<iostream>
#include<vector>
using namespace std;

typedef long long ll;
typedef long double ld;

ld res;

inline void check(ld x) {
	if (fabs(x) < res) res = fabs(x);
}

int main() {
	ll n, k, xbar;

	cin >> n >> k >> xbar;
	ll x[n];
	ll s = 0;
	for (int i = 0; i < n; i++) {
        cin >> x[i];
        x[i] -= xbar;
        s += x[i];
	}

	res = (ld)fabs(s) / n; // do not remove anything
	if (k >= 1) {
		for (int i = 0; i < n; i++)
			check((ld)(s - x[i]) / (n - 1));
	}
	if (k >= 2) {
		for (int i = 0; i < n; i++)
        for (int j = 0; j < i; j++)
            check((ld)(s - x[i] - x[j]) / (n - 2));
	}
	if (k >= 3) {
		for (int i = 0; i < n; i++)
        for (int j = 0; j < i; j++)
        for (int k = 0; k < j; k++)
            check((ld)(s - x[i] - x[j] - x[k]) / (n - 3));
	}
	if (k >= 4) {
		for (int i = 0; i < n; i++)
        for (int j = 0; j < i; j++)
        for (int k = 0; k < j; k++)
        for (int l = 0; l < k; l++)
            check((ld)(s - x[i] - x[j] - x[k] - x[l]) / (n - 4));
	}

	cout << res << endl;
}