abc011_D.py

from math import lgamma, exp, log
lfact = lambda n: lgamma(n + 1)
lcomb = lambda n, r: lfact(n) - lfact(n - r) - lfact(r)
 
n, d = map(int, input().split())
x, y = map(abs, map(int, input().split()))
if x % d != 0 or y % d != 0:
    print('0')
    exit(0)
x //= d
y //= d
r = 0
for u in range(n + 1):
    v = n - u
    if u - x < 0 or (u - x) % 2 != 0:
        continue
    if v - y < 0 or (v - y) % 2 != 0:
        continue
    t = lcomb(n, u) - 2*n * log(2)
    t += lcomb(u, x + (u - x) // 2)
    t += lcomb(v, y + (v - y) // 2)
    r += exp(t)
print(r)