#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    cur_price = p
    bought = 0
    while s >= cur_price:
        bought += 1
        s -= cur_price
        cur_price -= d
        if cur_price <= m:
            cur_price = m
    return bought

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)