# π的精度要求很高，记不到的话可以用求π的公式
#include <stdio.h>
#include <math.h>
#define PI 3.14159265358979323
int main()
{
	int r;
	double s;
	scanf("%d",&r);
	s = pow(r,2)*PI;
	printf("%.7lf",s);
	return 0;
	
}

#include<iomanip>
#include<math.h>

#define PI acos(-1)

using namespace std;

int main(){
	int r;
	cin >> r;
	cout << setiosflags(ios::fixed)<<setprecision(7) << PI * r * r << endl;
}

#include <cmath>
#include <iostream>
using namespace std;
int main()
{
    double pi;
    pi = atan(1) * 4;
    int r = 0;
    cin >> r;
    double s = r * r * pi;
    printf("%.7f",s);
    cout << endl;
    return 0;
}

#include <stdio.h>
#include <algorithm>
#include <math.h>
int main() {
    int  x,y;
    double pi=atan(1)*4,k=1,q=1.0/k;
    int tmp=-1;
    scanf("%d",&x);
    double s=pi*x*x;
    printf("%.7lf\n",s);
    return 0;
}