import java.io.*;
import java.util.*;

class Main89 {
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		double c = Double.parseDouble(br.readLine());
		String[] line = br.readLine().split(" ");
		double in = Double.parseDouble(line[0]);
		double out = Double.parseDouble(line[1]);
		
		System.out.println(1.0 / 4.0 * Math.pow(Math.PI, 2) * (in + out) * Math.pow(out - in, 2) * c);
	}
}