import java.util.*;
public class main{
    public static void main(String[] args) {
        try{
            int a,b,c,d,e,f;
            Scanner in=new Scanner(System.in);
            a=in.nextInt();
            b=in.nextInt();
            c=in.nextInt();
            d=in.nextInt();
            in.close();
            e=b;
            f=1;
            while(e<a)
            {
            	e+=c;
            	if(e>=a)
            	{
            		System.out.print(f);
            		break;
            	}
            	e-=d;
            	f++;
            }
            
        }catch(Exception e){
            System.out.println("Input error!");
        }
    }
};