mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    A = list(map(int, input().split()))
    R = list(map(int, input().split()))

    ans = 0
    for i0, a0 in enumerate(A):
        dp = [[0.] * (i+1) for i in range(N+1)]
        dp[0][0] = 1.
        for i, a in enumerate(A):
            r = R[i]
            for j in range(i+1):
                if a > a0 or (a == a0 and i >= i0):
                    dp[i+1][j] = (dp[i+1][j] + dp[i][j] * 0.5)
                    if j:
                        dp[i+1][j-1] = (dp[i+1][j-1] + dp[i][j] * 0.5)
                    else:
                        if i >= i0:
                            ans += r * a0 * dp[i][j] * 0.5
                        else:
                            dp[i+1][j] = dp[i+1][j] + dp[i][j] * 0.5
                else:
                    dp[i + 1][j] = (dp[i + 1][j] + dp[i][j] * 0.5)
                    dp[i+1][j+1] = (dp[i+1][j+1] + dp[i][j] * 0.5)
    print(ans)


if __name__ == '__main__':
    main()