Python input/output boilerplate for competitive programming

The following code is my submission for Codeforces 1244C The Football Season.

import io
import sys
import math

def inverse(a,m):
    u = 0
    v = 1
    while a != 0:
        t = m // a
        m -= t * a
        a,m = m,a
        u -= t * v
        u,v = v,u
    assert m == 1
    return u

def main():
    # It helps to use a input file when testing or debugging your code locally.
    # with open("main.in","r",encoding='utf-8') as f:
    with sys.stdin as f:
        n,p,w,d = map(int,f.readline().split())
        g = math.gcd(w,d)
        if p % g:
            print(-1)
            return
        W = w // g
        D = d // g
        x = inverse(W,D)
        y = (1 - W * x) // D
        assert W * x + D * y == 1
        m = p // g
        x *= m
        y *= m
        ub = min(x // D,(n - x - y) // (W - D))
        lb = (-y + W - 1) // W
        if lb > ub:
            print(-1)
            return
        X = x - lb * D
        Y = y + lb * W
        assert X >= 0 and Y >= 0 and X * w + Y * d == p and X + Y <= n
        print(X,Y,n - X - Y)
main()

Notes:

1. // does floor divison in Python.