# binomialSum.py
# inputs: 200 0.45 0 80  or 2nd value == 0.47, 0.471

import math
from binomial import *

n,p,c,d = map(float, input("n p c d=? ").split())
n = int(n)
c = int(c); d = int(d)
sum = 0
for x in range(c, d+1):
  sum += binomial(n, p, x)
print(f"{sum:.8f}")