#include <bits/stdc++.h>
using namespace std;
int main()
{
	int C,I,O;
	cin >> C >> I >> O;
	double sum = ( O - I ) / 2.0;
	cout << fixed << setprecision(10) <<
		sum * sum * M_PI * ( ( I + sum ) * 2 ) * M_PI * C  << endl;
	return 0;
}