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

void no_89(void) {
    int c, rin, rout;
    cin >> c >> rin >> rout;
    const double PI = 3.141592653;

    double v = (rin + rout) * pow((rout - rin), 2.0);
    double ans = c * v * pow(PI,2.0) / 4;

    printf("%0.16f\n", ans);
}

int main(void) {
    no_89();
    return 0;
}