n = int(input())
k = int(input())
a = [(int)0 for i in range(n)]
b = [(float)0 for i in range(n)]
db =[(float)0 for i in range(n)]
elems = [[] for i in range(k+1)]

sumdB = (float)0
squared_sumdB = (float)0

def GetD():
    sm = (float)0
    for i in range(n):
        sm += b[i]
    sm /= n
    for i in range(n):
        db[i] = b[i] - sm
        sumdB += db[i]
        squared_sumdB += db[i] * db[i]
    squared_sumdB = sqrt(squared_sumdB)

def CorrelationCoef(e):
    sm = (float)len(e)
    sm2 = 1 - sm
    sm *= -1
    sumC = sm * sumdB
    sumZ = sqrt(sm * sm * (n - len(e)) + sm2 * sm2 * len(e))
    sumZ *= squared_sumdB
    for u in e:
        sumC -= sm * db[u]
        sumC += sm2 * db[u]
    return sumC / sumZ

for i in range(n):
    a[i] = int(input())
    elems[a[i]].append(i)

for i in range(n):
    b[i] = int(input())

GetD()
smC = (float)0

for i in range(1, k+1):
    if(len(elems[i]) > 0):
        smC += len(elems[i]) * CorrelationCoef(elems[i])

print(smC)