/**
    斐波那契數列數列，遞迴超時
    採用陣列解決。
*/
import java.util.*;
public class Main{
	public static long Fib(long i) {
		if(i==1)
			return 1;
		else if(i==2)
			return 1;
		else {
			return (Fib(i-1)+Fib(i-2))%10007;
		}
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int data[] = new int[N];
		data[0] = 1;
		if(N>1)
			data[1] = 1;
		for(int i=2;i<N;i++)
			data[i] = (data[i-1]+data[i-2])%10007;
		System.out.println(data[N-1]);
		
	}
}
 

/**
    注意輸出格式以及常量的定義
*/
import java.util.*;
public class Main{
	public static final double PI = 3.14159265358979323;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double r = sc.nextDouble();
		System.out.printf("%.7f\n", r*PI*r);
	}
}

/**
    注意資料輸入的範圍
    1 <= n <= 1,000,000,000。
*/
import java.util.*;
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextInt();
		System.out.println(N*(N+1)/2);
	}
}