def log_prior(H0, od0, c, b, M):
    if  not 0.68 < od0 < 0.70 and  60 < H0 < 80  and   -20 < M < -18.5 and 0.045 < b < 0.065 :
        #return 0.0
        return -np.inf
    mu = 0.878
    sigma = 0.0004
    return np.log(1.0/(np.sqrt(2*np.pi)*sigma))-0.5*(c-mu)**2/sigma**2