#!/bin/python3

import sys

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

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)