#include<bits/stdc++.h>
using namespace std;
int main(){	
int n,r;
cin>>n>>r;
float Y;
cin>>n>>r;
Y=n*n*3.14-r*r*3.14;
printf("%.2f",Y); 
	return 0;
}


/**************************************************************
	Problem: 1338
	User: lidongbo
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/