#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    money = s
    price = p
    count = 0
    while money >= price:
        money -= price
        count += 1
        price -=  d
        if price < m:
            price = m
    return count

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)