from itertools import accumulate, pairwise
from bisect import bisect_left


def bsearch(low: int, high: int, pred) -> int:
    assert pred(low)
    lo = low
    hi = high
    res = low
    while lo <= hi:
        m = (lo + hi) // 2
        if pred(m):
            res = max(res, m)
            lo = m + 1
        else:
            hi = m - 1

    return res


INF = 1 << 62
N, L = map(int, input().split())
K = int(input())
A = list(map(int, input().split()))


cakes = []
for a, b in pairwise([0] + A + [L]):
    cakes.append(b-a)

acc = list(accumulate(cakes))


# 2番目に大きな値を m 以上にできるか
def can(m: int) -> bool:
    sz = len(cakes)
    dp = [[-INF] * 3 for _ in range(sz+1)]
    dp[0][0] = 0
    for i in range(sz):
        for j in range(3):
            dp[i+1][j] = max(dp[i+1][j], dp[i][j] + 1)

        # i 番目から総和が m を超える最小の p
        x = acc[i-1] if i > 0 else 0
        p = bisect_left(acc, x + m)
        if p < sz:
            for j in range(3-1):
                dp[p+1][j+1] = max(dp[p+1][j+1], dp[i][j] + 1)

    return dp[sz][2] > K


ans = bsearch(1, L, can)
print(ans)