import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
{
Scanner in
=new Scanner
(System.
in); double a=in.nextDouble();
int p=in.nextInt();
double xz=in.nextDouble();
double eps=in.nextDouble();
double x
=Math.
pow(a,
1.0/p
); double xn=xz,x_prev=-10000000;
int i=0;
while (Math.
abs(xn
-x_prev
)>=eps
) {
x_prev=xn;
xn
=(x_prev
/(p
*p
))*((p
*p
-1)+0.5*(p
+1)*a
/(Math.
pow(x_prev,p
))-0.5*(p
-1)*Math.
pow(x_prev,p
)/(a
)); i++;
}
}
}
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