import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner in = new Scanner(System.in);
		double k,p,s,n,y;
		k=in.nextDouble();
		p=in.nextDouble();
		s=in.nextDouble();
		n=in.nextDouble();
		if ((k<=0)||(p<=0)||(s<=0)||(n<=0)) {System.out.printf("Неверные денные");} 
		else {
			double l1=Math.log(n*s/k);
			double l2=Math.log(p);
			y = Math.ceil(l1/l2); 
			System.out.printf("%.0f",y);
		}
	}
}

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NiAJMTAgCTIwIAk0MSAJMw==

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