import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Arrays;
import java.util.Set;

import java.util.concurrent.ThreadLocalRandom;
class he
{
 
 
	
	public static void main(String []args)
	{
		Scanner in = new Scanner(System.in);
		Scanner haha = new Scanner(System.in);

    int p = in.nextInt();
    int d = in.nextInt();
    int m = in.nextInt();
    int total = in.nextInt();
    int sum = 0;
    int count=0;
    for(int i=p;true;){
    	sum+=i;
    	count++;
    	if(sum>total){
    		count--;
    		break;
    	}if(sum==total){
    		break;
    	}
    	if(i-d>=m)
    		i = i-d;
    	else if(i-d<m)
    		i=m;
    	
    }
    System.out.println(count);
	}
	
}