#!/bin/python3

import sys

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

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)