import java.util.Scanner;
import java.util.stream.IntStream;

public class Main{
	static IntStream REPS(int v){return IntStream.range(0,v);}
	static IntStream REPS(int l,int r){return IntStream.rangeClosed(l,r);}
	static IntStream INS(int n){return REPS(n).map(i->getInt());}
	static Scanner s=new Scanner(System.in);
	static int getInt(){return Integer.parseInt(s.next());}
	static long getLong(){return Long.parseLong(s.next());}

	public static void main(String[]$){
		int c=getInt(),rin=getInt(),rout=getInt();
		double rs=(rout-rin)/2.0;
		System.out.println(c*Math.PI*(rout+rin)*rs*rs*Math.PI);
	}
}