n,c=map(int,input().split())
li=sorted([int(x) for x in input().split()])
def ch(g):
    ck,la=1,li[0]
    for gx in li[1:]:
        if gx-la>=g:
            ck+=1
            la=gx
    return ck>=c
l,r=0,li[-1]-li[0]
while l<=r:
    mid=l+r>>1
    if ch(mid):l=mid+1
    else:r=mid-1
print(l-1)