#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    //p=cost of game, d=reducing factor  ,m=base cost after which not reducing  ,s= money in wallet   20 3 6 80
    if(s==0)
    return 0;
    int flag=0;
    d=0;
    while(s>=m)
    {
        p-=d;	
		flag++;
		s-=p;
		d=3;   
	}
	return flag;
}

int main() {
    int p; 
    int d; 
    int m; 
    int s; 
    scanf("%i %i %i %i", &p, &d, &m, &s);
    int answer = howManyGames(p, d, m, s);
    printf("%d\n", answer);
    return 0;
}