#!/bin/python

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    cnt = 0 
    scost = 0
    tp = p
    while scost + tp <= s:
        scost += tp
        cnt += 1
        tp = max(tp - d, m)
    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