#include<algorithm>
#include<cassert>
#include<cmath>
#include<set>
#include<iostream>
#include<numeric> // accumulate
#include<vector>
using namespace std;

typedef long long ll;
typedef long double ld;

ld res;

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

ld solve() {
	ll n, k, xbar;
	vector<ll>::iterator it;

	cin >> n >> k >> xbar;
	vector<ll> x(n);
	for (ll &xi : x) cin >> xi;
	for (ll &xi : x) xi -= xbar; // set xbar = 0 WLOG
	sort(x.begin(), x.end());

	ll s = accumulate(x.begin(), x.end(), 0LL);

	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) {
		multiset<long long> cantake;
		for (int i = 0; i < n; i++) {
			cantake.insert(x[i]);
		}

		for (int i = 0; i < n; i++) {
			// now we cannot remove something that uses index i (or before)
			cantake.erase(cantake.find(x[i]));

			for (int j = 0; j < i; j++) {
				ll goal = s - x[i] - x[j];
				auto it = cantake.lower_bound(goal);
				if (it != cantake.end()) {
					check((ld)(goal - *it) / (n - 3));
				}
				if (it != cantake.begin()) {
					check((ld)(goal - *--it) / (n - 3));
				}
			}
		}
	}
	if (k == 4) {
		multiset<long long> cantake;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < i; j++) {
				cantake.insert(x[i] + x[j]);
			}
		}

		for (int i = 0; i < n; i++) {
			// now we cannot remove something that uses index i (or before)
			for (int j = i + 1; j < n; j++)
				cantake.erase(cantake.find(x[i] + x[j]));

			for (int j = 0; j < i; j++) {
				ll goal = s - x[i] - x[j];
				auto it = cantake.lower_bound(goal);
				if (it != cantake.end()) {
					check((ld)(goal - *it) / (n - 4));
				}
				if (it != cantake.begin()) {
					check((ld)(goal - *--it) / (n - 4));
				}
			}
		}
	}

	assert(k <= 4); // k >= 5 not supported
	return res;
}

int main() {
	(cout << fixed).precision(9);
	cout << solve() << endl;
}