#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy 
    if s < p:
        return 0
    if d == 0:
        return s // p
    n_bargains = (p-m) // d + 1
    average_bargain_cost = (p + p - (n_bargains-1) * d)/2
    remainder = s - n_bargains * average_bargain_cost
    if remainder >= 0:
        return int(n_bargains + remainder // m)
    else:
        n_bargains = max([i for i in range(0, s // d) if s - i*((p + p-(i-1)*d) / 2) >= 0])
        return int(n_bargains)
        

if __name__ == "__main__":
    p, d, m, s = input().strip().split(' ')
    p, d, m, s = [int(p), int(d), int(m), int(s)]
    answer = howManyGames(p, d, m, s)
    print(answer)