#!/bin/python

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    # m is min, p = first price
    # d is diff
    # s is the input number of dollars
    total = 0
    curr_price = p
    curr_dollars = s
    while curr_price <= curr_dollars:
        curr_dollars -= curr_price
        curr_price = max(m, curr_price - d)
        total += 1
    return total
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