N = int(raw_input())
K = int(raw_input())

n = []

for i in range(N):
    n.append(int(raw_input()))

n.sort()
grp=[]
for i in range(K):
    grp.append(0)


grp[0] = n[0]

for i in range(0,N-2):
    grp[i%K]=n[i]

grp[K-1]=n[N-1]

    
ans = str(grp[K-1] - grp[0])

print ans