#include <iostream>
#include <iomanip>

using ldouble = long double;
constexpr ldouble PI = 3.14159265358979L;

void solve() {
    ldouble c, p, q;
    std::cin >> c >> p >> q;

    auto r = (q - p) / 2,
         s = (p + q) / 2;

    std::cout << std::fixed << std::setprecision(10)
              << 2 * PI * s * PI * r * r * c << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}