Submission #188141

---

Source Code Expand

#!/usr/bin/env python

import decimal


def read():
    N, D = map(int, raw_input().split())
    X, Y = map(int, raw_input().split())
    return (N, D, X, Y)


def work((N, D, X, Y)):
    total = 0
    
    for nU in range(N + 1):
        for nD in range(N + 1 - nU):
            if nU * D - nD * D != X:
                continue
            
            for nL in range(N + 1 - nU - nD):
                nR = N - nU - nD - nL

                if nR * D - nL * D != Y:
                    continue
                    
                def count(A, B, C, D, n):
                    def f(v):
                        ret = 1
                        for i in range(1, v + 1):
                            ret *= i
                        return ret

                    return f(n) / f(A) / f(B) / f(C) / f(D)
                    
                total += count(nU, nD, nL, nR, N)

    print "%.15f" % (decimal.Decimal(total) / decimal.Decimal(4 ** N))


if __name__ == "__main__":
    work(read())

Submission Info

Judge Result