def M(L):
    S=0
    for x in L:
        S=S+x
    m=S/len(L)
    return m

def Reg(X,Y):
    mx=M(X)
    X=[x-mx for x in X]
    my=M(Y)
    Y=[y-my for y in Y]
    n=len(X)
    V=0
    C=0
    for i in range(n):
        V=V+X[i]**2
        C=C+X[i]*Y[i]
    a=C/V
    return a