#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    if p > s:
        return 0

    steps = (p - m) // d
    pre = (p + p - d * steps)  * (steps + 1) // 2
    if pre > s:
        i = 0
        while s >= p:
            s -= p
            p -= d
            i += 1
        return i
        #a = -d
        #b = 2 * p - d
        #c = 2 * s
        #return -(int((-b + (b * b - 4 * a * c) ** 0.5) // (2 * a)))
    else:
        return (s - pre) // m + steps + 1

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)