招聘会小礼品

	def prizeGetFunc(N,M,C,P):
    """"
    Parameters
    ----------
    N :   number of interviewees
    M :   kinds of the gifts
    C :   number of each gift
    P :   preferential matrix
    """
    leftPrize = 0     # initiate the number of prizes left
    for j in range(M):
        if C[j] < 1:
            prizeLeftPro = [0]
        else:
            prizeLeftPro = [0]*C[j]+[1]  # initialize the left prob of each prize (from 0 to C[j])
            for i in range(N):
                    prizeLeftPro[0] += prizeLeftPro[1] * P[i][j] # left 0, prizes of kind i are all given
                    for k in range(C[j]):
                        prizeLeftPro[k] = prizeLeftPro[k]*(1-P[i][j]) + prizeLeftPro[k+1]*P[i][j] # update the p_k
                    prizeLeftPro[C[j]] = prizeLeftPro[C[j]]*(1-P[i][j])
        for k in range(1,C[j]+1):
            leftPrize += prizeLeftPro[k]*k # calculate the expected number of prizes left
    getPrize = round(N-leftPrize,2) 
    return getPrize

N,M = map(int,raw_input().split())
C = map(int,raw_input().split())
P = [map(float,raw_input().split()) for i in range(N)]
getPrize = prizeGetFunc(N,M,C,P)
print getPrize