import java.lang.Math;
public class ppp {
			
  public static void main(String[] args) {
	  MyScanner sc=new MyScanner();
	  double c=sc.nextInt();
	  double nai=sc.nextInt();
	  double gai=sc.nextInt();
	  double a=(gai-nai)/2;
	  double b=(nai+gai)/2;
	  System.out.println(2*c*a*a*b*Math.PI*Math.PI);
	  
}
}

class MyScanner {
	int nextInt() {
		try {
			int c = System.in.read();
			while (c != '-' && (c < '0' || '9' < c))
				c = System.in.read();
			if (c == '-')
				return -nextInt();
			int res = 0;
			do {
				res *= 10;
				res += c - '0';
				c = System.in.read();
			} while ('0' <= c && c <= '9');
			return res;
		} catch (Exception e) {
			return -1;
		}
	}

	double nextDouble() {
		return Double.parseDouble(next());
	}

	long nextLong() {
		return Long.parseLong(next());
	}

	String next() {
		try {
			StringBuilder res = new StringBuilder("");
			int c = System.in.read();
			while (Character.isWhitespace(c))
				c = System.in.read();
			do {
				res.append((char) c);
			} while (!Character.isWhitespace(c = System.in.read()));
			return res.toString();
		} catch (Exception e) {
			return null;
		}
	}
}