N,L=map(int,input().split())
K=int(input())
A=list(map(int,input().split()))
A=[0]+A[:]+[L]
l=1
r=L
from bisect import bisect_right
while True:
  if l==r:
    break
  m=(l+r+1)//2
  v0=[10**10]*(N+2)
  v1=[10**10]*(N+2)
  for i in range(1,N+2):
    x=A[i]
    pos=bisect_right(A,x-m)
    v0[i]=min(v0[i],v0[i-1])
    v1[i]=min(v1[i],v1[i-1])
    if pos==0:
      continue
    cost=i-pos
    v0[i]=min(v0[i],cost)
    v1[i]=min(v1[i],cost+v0[pos-1])
  if v1[N+1]<=N-K:
    l=m
  else:
    r=m-1
print(l)