import sequtils,strutils,math
var
    N = stdin.readline.parseInt
    A = stdin.readline.split.map(parseInt)
    B = stdin.readline.split.map(parseInt)
    hyou : array[17, array[17, array[5, int]]]
hyou[0][0][0] = 1
for i in 0..<(1 shl N):
    for j in 0..<(1 shl N):
        var
            ibit = countBits32(i.int32)
            jbit = countBits32(j.int32)
        if ibit != jbit:
            continue
        for a in 0..<N:
            for b in 0..<N:
                if (i and (1 shl a)) == 0 and (j and (1 shl b)) == 0:
                    if A[a] > B[b]:
                        for k in 0..<N:
                            #echo @[i,j,a,b,(j or (1 shl b))]
                            hyou[i or (1 shl a)][j or (1 shl b)][k + 1] += hyou[i][j][k]
                    else:
                        for k in 0..<N:
                            hyou[i or (1 shl a)][j or (1 shl b)][k] += hyou[i][j][k]
                        
var
    k : int
    p : int = 1

for i in 1..N:
    if i > (N - i):
        k += hyou[(1 shl N) - 1][(1 shl N) - 1][i]

for i in 1..N:
    p *= i

var ans : float64 = k / (p * p)
echo ans