N,L = map(int,input().split())
K = int(input())
A = [0]+list(map(int,input().split()))+[L]
N+=2

def check(X): # X以上のyokanを2個以上作れるか？
  r = 0
  p = [-1]*N
  for l in range(N):
    while r < N and A[r]-A[l]<X:
      r += 1
    p[l] = r
  
  dp = [[-float("inf")]*3 for i in range(N)]
  dp[0][0] = 0
  for i in range(N-1):
    for k in range(3):
      dp[i+1][k] = max(dp[i+1][k], dp[i][k]+1)
      if k != 2 and p[i] != N:
        dp[p[i]][k+1] = max(dp[p[i]][k+1], dp[i][k]+1)
  
  return (dp[N-1][2] >= K+1)
      

ok = 1
ng = L

while ng - ok > 1:
  mid = (ok+ng)//2
  if check(mid):
    ok = mid
  else:
    ng = mid

print(ok)