#define _USE_MATH_DEFINES
#include <iostream>
#include <iomanip>
#include <map>
#include <stack>
#include <vector>
#include <string>
#include <cmath>
using namespace std;
const int MOD = 1e9 + 7;

int main(){
    int c, in, out;
    cin >> c >> in >> out;

    double radius = (out - in) / 2.;
    double ans = radius * radius * M_PI * (in + radius) * 2 * M_PI * c;
    cout << fixed << setprecision(10) << ans << endl;
}