using System;

public class Program {
	public static void Main() {
		double c = int.Parse(Console.ReadLine());
		string[] s = Console.ReadLine().Split(' ');
		double rin = int.Parse(s[0]);
		double rout = int.Parse(s[1]);
		double r = (rout - rin) / 2;
		double R = (rout + rin) / 2;
		double PI = Math.PI;
		
		// 体積 ＝（切り口の円の面積）πｒ² ×（大円の周の長さ）２πＲ
		double ans = r * r * PI * 2 * PI * R * c;
		
		Console.WriteLine(ans);
	}
}