n=int(input())
k=int(input())
lst=[int(input()) for _ in range(n)]
m=(n+k-1)//k
m_r=n%k
kk=[m]*k if m_r==0 else [m]*(k-1)+[m_r]
print(lst,kk)
def zin():
    i=0
    ans_lst=[]
    while(i<n):
        for j in kk:
            tmp=sum(lst[i:i+j])
            i+=j
            ans_lst.append(tmp/j if j!=0 else 0)
    return max(ans_lst)-min(ans_lst)
print(zin())