import strutils,sequtils,algorithm
var
    L : seq[int]
    N,M,Ma,mi,n : int
    A,A2 : seq[int]
    k : int
    I,p,cnt,point,j,index : int
A = @[]
L = stdin.readline.split.map(parseInt)
(N,M) = (L[0],L[1])
I = stdin.readline.parseInt
for n in 0..<N - 1:
    k = stdin.readline.parseInt
    A.add(k)
A.sort(system.cmp)
Ma = N - 1
mi = 0
while Ma - mi > 0:
    n = (Ma + mi) div 2
    p = A[n]
    point = I + p
    A2 = reversed(A[0..n-1] & A[n + 1..high(A)])
    cnt = 0
    block hantei:
        var right = A2.high
        for i,a in A2:
            for j in countdown(right,i):
                if j == i:
                    break hantei
                if a + A2[j] > point:
                    right = j - 1
                    cnt += 1
                    break
    if cnt >= M:
        mi = n + 1
    if cnt < M:
        Ma = n
    if Ma <= N - 2 and A[mi] == A[Ma]:
        break
if mi > N - 2:
    echo -1
else:
    echo A[mi]