N,C=map(int,input().split())
position=[]
for _ in range(N) :
    position.append(int(input()))
    position.sort()
left=0
right=position[-1]-position[0]
mid=0
def p(C,distance) :
    count=1
    positions=position[0]
    for i in position :
         if i-positions>=distance :
             count+=1
             positions=i
             if count>=C :
                 return  True
    return False


while left < right :
    mid=(left+right+1)//2
    if p(C,mid) :
        left=mid
    else :
        right=mid+1
print(right)