N, L = map(int, input().split())
K = int(input())
A = list(map(int, input().split()))

INF = 1<<60

def func(limit):
    R = []
    r = 0
    for l in range(N+1):
        while r < len(A) and A[r]-A[l] < limit:
            r += 1
        R.append(r)
    dp = [[-INF]*3 for _ in range(N+2)]
    dp[0][0] = 0
    for i in range(N+1):
        for j in range(3):
            if dp[i][j] == -INF: continue
            dp[i+1][j] = max(dp[i+1][j], dp[i][j]+1)
            if R[i] <= N+1 and j < 2:
                dp[R[i]][j+1] = max(dp[R[i]][j+1], dp[i][j]+1)
    return K+1 <= dp[-1][2]

A = [0]+A+[L]

left = 0
right = 10**9
while left+1 < right:
    mid = (left+right)//2
    if func(mid):
        left = mid
    else:
        right = mid

print(left)