n, l = list(map(int, input().split()))
k = n-int(input())
A = [0] + list(map(int, input().split())) + [l]
from bisect import bisect_right as bs1
from bisect import bisect_left as bs0
r = l+1
l = 0
inf = 1 << 30
def main(x):
    #print(x, "X")
    dp = [inf] * (n+1)
    for i in range(1, n+1):
        dp[i] = dp[i-1]
        if A[i] < x:
            continue
        j = bs1(A, A[i]-x)
        dp[i] = min(dp[i], i-j)
    now = inf
    for i in range(n, -1, -1):
        if A[-1] - A[i] < x:
            continue
        j = bs0(A, A[i]+x)
        now = min(now, j-i-1)
        if now + dp[i] <= k:
            return 1
    return 0
    

while r - l > 1:
    m = (l + r) >> 1
    if main(m):
        l = m
    else:
        r = m

print(l)