import bisect

n,m = map(int,input().split())
k = int(input())
A = [int(_) for _ in input().split()]
A = [0] + A + [m]
def check(num):
  S = [10**18] * (n+1)
  for i in range(n+1):
    left = i
    right = bisect.bisect_left(A,A[left] + num)
    if right == n+2:
      S[left] = 10**18
      continue
    S[left] = right - left
  min_S = [10**18] * (n+1)
  min_S[-1] = S[-1]
  for i in range(n):
    min_S[-(i+2)] = min(min_S[-(i+1)],S[-(i+2)])
  for i in range(n):
    if S[i] == 10**18 or i+S[i]+1 >= n+1:
      continue
    if (n + 1) - ( S[i] + min_S[i + S[i] + 1] ) >= k - 1:
      return True
  return False
left = 0
right = 10**10
while left + 1 != right:
  mid = (left+right) // 2
  if check(mid):
    left = mid
  else:
    right = mid
print(left)