#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    k=int((p-m)/d)
    ans=0
    if (k+1)*p-k*(k+1)/2*d<s:
        left=s-(k+1)*p+k*(k+1)*d/2
        ans=k+1
        while left>=0:
            left=left-m
            ans=ans+1
        ans=ans-1
        return ans
    else:
        left=s
        for j in range(k+1):
            left=left-p+j*d
            if left>=0:
                ans=ans+1
            else:
                return ans

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)