#include <bits/stdc++.h>
using namespace std;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);  
	
	double c, r_in, r_out; cin >> c >> r_in >> r_out;
	double pi = acos(-1);
	double ans = 1;
	ans *= pow((r_out - r_in) / 2, 2) * pi;
	ans *= 2 * pi * (r_in + r_out) / 2;
	cout << setprecision(20) << c * ans << endl;
	return 0;	
}