import itertools
def l(a,i,r):
    s=[b for b in r if a[i][b]]
    k=len(s)
    return 2.0*sum(map(lambda x:a[x[0]][x[1]],itertools.combinations(s,2)))/k/(k-1)
def g(a):
    n=len(a)
    r=range(n)
    return sum([l(a,i,r) for i in r])/n

print g([[0,1,1],
         [1,0,0],
         [1,0,0]])