#include <iostream>
#include <iomanip>
#include <cmath>

using ldouble = long double;

const ldouble PI = std::acos(-1.L);

void solve() {
    ldouble a, b;
    std::cin >> a >> b;
    std::cout << std::fixed << std::setprecision(10)
              << PI * (b - a) * 2 << "\n";
}

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

    solve();

    return 0;
}