import sys

read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

readlines = sys.stdin.buffer.readlines



N,D,X = list(map(int,read().split()))



answer = 0

for n in range(N,0,-1):

    mean = D + X * (n+n-1) / 2

    answer += mean

    D = ((n+n+2) * D + 5 * X) / (2*n)

    X = (n + 2) * X / n



print(answer)
import sys



read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

readlines = sys.stdin.buffer.readlines



N, d, x = list(map(int, read().split()))



def main(N, d, x):

    ret = 0

    while N:

        ret += d + (N-0.5) * x

        d = d + (d/N) + (5*x)/(2*N)

        x += 2*x/N

        N -= 1

    return ret



print((main(N, d, x)))
import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
N, D, X = list(map(int, read().split()))
answer = 0
for n in range(N, 0, -1):
    mean = D + X * (n + n - 1) / 2
    answer += mean
    D = ((n + n + 2) * D + 5 * X) / (2 * n)
    X = (n + 2) * X / n
print(answer)

import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
N, d, x = list(map(int, read().split()))


def main(N, d, x):
    ret = 0
    while N:
        ret += d + (N - 0.5) * x
        d = d + (d / N) + (5 * x) / (2 * N)
        x += 2 * x / N
        N -= 1
    return ret


print((main(N, d, x)))

-N, D, X = list(map(int, read().split())) -answer = 0 -for n in range(N, 0, -1): -    mean = D + X * (n + n - 1) / 2 -    answer += mean -    D = ((n + n + 2) * D + 5 * X) / (2 * n) -    X = (n + 2) * X / n -print(answer) +N, d, x = list(map(int, read().split())) + + +def main(N, d, x): +    ret = 0 +    while N: +        ret += d + (N - 0.5) * x +        d = d + (d / N) + (5 * x) / (2 * N) +        x += 2 * x / N +        N -= 1 +    return ret + + +print((main(N, d, x)))