#!/bin/python3

import sys

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
    k=(p-m)/d
    
    if k%1 !=0:
        k=int(k)+1
        
    cost=0
    count=0
    i=0
    while cost<s:
        if count<k:
            cost+=p-i*d
        else:
            cost+=m
        count+=1
        i+=1
    r=0
    if cost==s:
        r=count
    elif cost>s:
        r=count-1
    
    return r
        
            
        

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)