#t = int(input())
t = 1
for _ in range(t):
  n,l = map(int, input().split())
  k = int(input())
  a = [0] + list(map(int, input().split())) + [l]
  from bisect import bisect_left
  cur = bisect_left(a,l/2)
  if l/2 - a[cur-1] < a[cur]-l/2:
    cur -= 1
  li = []
  r = []
  for i in range(cur+1):
    li.append(a[i])
  for i in range(cur,n+2):
    r.append(a[i]-a[cur])

  ll,lr,rl,rr = 0,len(li)-1,0,len(r)-1
  for i in range(k-1):
    if ll != lr:
      m1 = min(li[lr]-li[ll+1],r[rr]-r[rl])
      m2 = min(li[lr-1]-li[ll],r[rr]-r[rl])
    else:
      m1 = -10**18
      m2 = -10**18
    if rl != rr:
      m3 = min(li[lr]-li[ll],r[rr]-r[rl+1])
      m4 = min(li[lr]-li[ll],r[rr-1]-r[rl])
    else:
      m3 = -10**18
      m4 = -10**18
    ma = max(m1,m2,m3,m4)
    if ma == m1:
      ll += 1
    elif ma == m2:
      lr -= 1
    elif ma == m3:
      rl += 1
    else:
      rr -= 1
    #print(li,r,ll,lr,rl,rr)
  ma = min(li[lr]-li[ll],r[rr]-r[rl])
  print(ma)