#!/bin/python

import sys

def howManyGames(p, d, m, s):
    r = range(p, m - 1, -d)
    c = 0
    for x in r:
        if x > s:
            return c
        c += 1
        s -= x
    while s >= m:
        c += 1
        s -= m
    return c


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