#!/bin/python

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    c=0
    rate=0
    cost=1
    while (cost<=s):
        if(c==1):
            rate=p
            c+=1
        elif (c>1):
            for i in range(c):
                if (rate>=m):
                    rate=m
                    c+=1
                else:
                    rate=rate+(p-d)
                    c+=1
    cost= cost+rate
    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