import sys
input = sys.stdin.readline

from bisect import bisect_left

N,L=list(map(int,input().split()))
K=int(input())
A=list(map(int,input().split()))


A=[0]+A+[L]

OK=1
NG=L+1

while NG>OK+1:
    mid=(OK+NG)//2

    DP0=[0]*len(A)
    DP1=[-100]*len(A)
    DP2=[-100]*len(A)

    for i in range(len(A)-1):
        x=DP0[i]
        DP0[i+1]=max(DP0[i+1],x+1)
        k=bisect_left(A,A[i]+mid)

        if k<len(A):
            DP1[k]=max(DP1[k],x+1)

        x=DP1[i]
        DP1[i+1]=max(DP1[i+1],x+1)

        if k<len(A):
            DP2[k]=max(DP2[k],x+1)

        x=DP2[i]
        DP2[i+1]=max(DP2[i+1],x+1)

    if DP2[-1]>=K+1:
        OK=mid
    else:
        NG=mid

    #print(mid)
    #print(DP0)
    #print(DP1)
    #print(DP2)

print(OK)