#!/bin/python

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    count = 0
    price = p
    while s >= price:
      s -= price
      price -= d
      count += 1
      if price < m:
        price = m
    return count    
if __name__ == "__main__":
    p, d, m, s = raw_input().strip().split(' ')
    p, d, m, s = [int(p), int(d), int(m), int(s)]
    answer = howManyGames(p, d, m, s)
    print answer