#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <numeric>
#include <optional>
#include <vector>

using namespace std;

int main() {
    int32_t c, rin, rout;
    cin >> c >> rin >> rout;
    double v = M_PI * M_PI * (rin + rout) * (rout - rin) * (rout - rin) / 4;
    printf("%.7f\n", v * c);
    return 0;
}