#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main() {
    double c, rin, rout;
    cin >> c >> rin >> rout;
    double ans = c * (rout - rin) * (rout - rin) / 4 * (rout + rin) * M_PI * M_PI;
    printf("%.6f\n",ans);
    return 0;
}