N,K = [int(input()) for x in range(2)]
lis = [int(input()) for x in range(N)]
lis.sort()
seplis = [[] for x in range(K)]
seplis[0].append(lis.pop(-1))
seplis[-1].append(lis.pop(0))
current = 1
while lis:
    seplis[current].append(lis.pop(0))
    current = (current + 1) % (K - 1)
    if not current:
        current = 1
_max = seplis[0][0]
_min = seplis[-1][0]
ans = _max - _min
print(ans)