#!/usr/bin/env python3

n, K, X = map(int, input().split())

xs = list(map(int, input().split()))
S = sum(xs)

pairs = []
for i in range(n):
    for j in range(i):
        pairs.append((xs[i] + xs[j], [i, j]))

# k = 0
best = abs(S / n - X)
if K >= 1:
    for s in xs:
        best = min(best, abs((S - s) / (n - 1) - X))
if K >= 2:
    for (s, ij) in pairs:
        best = min(best, abs((S - s) / (n - 2) - X))
if K >= 3:
    for (s1, ij) in pairs:
        for k, s2 in enumerate(xs):
            if k not in ij:
                best = min(best, abs((S - s1 - s2) / (n - 3) - X))
if K >= 4:
    for (s1, ij) in pairs:
        for (s2, [k, l]) in pairs:
            if k not in ij and l not in ij:
                best = min(best, abs((S - s1 - s2) / (n - 4) - X))

print(best)