def check(a, n, k, x):
    i = 0
    cnt = 0
    while i + 1 < n:
        if a[i+1] -a[i] <= x:
            cnt +=1
            i += 2
        else:
            i +=1
    if cnt >= k:
        return True
    else:
        return False
n, k = map(int, input().split())
a = list(map(int, input().split()))
a.sort()
low = 0
high = 10**9
res =-1
while low <= high:
    mid = (low + high) // 2
    if check(a, n, k, mid):
        res = mid
        high = mid -1
    else:
        low = mid + 1
print(res)