#include <bits/stdc++.h>
using namespace std;
int r1,r2;//r1外圆的R，r2内圆的R 
double s;
double const p=3.14;
int main(){
    cin>>r1>>r2;
    s=p*(r1*r1-r2*r2)*1.0;
    printf("%.2f",s);
	return 0;
}
/**************************************************************
	Problem: 1338
	User: zengdongxin
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/