#include <iostream>
#include <iomanip>

using namespace std;

int main() {
    int a, b, c;
    cin >> a >> b >> c;
    double t = a * b;  
    double t1 = 2 * b * c; 
    double rt2 = a * c;  
    double h = 0.5 * 3.1415926535 * (a / 2.0) * c;
	double ts = t + t1 + rt2 + h;
	double to = ts / 10000.0;
	cout << fixed << setprecision(3) << to << endl;

    return 0;
}