#!/bin/python

import sys


def howManyGames(p, d, m, s):
    cnt = 0
    i = 0
    
    prices = []
    while p > m:
        prices.append(p)
        p -= d
    prices += [m] * s
    #print prices
    #i = 0
    while s > 0:
        s -= prices[i]
        i += 1
        cnt += 1
    if s < 0:
        cnt -= 1
    return cnt


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