#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cout.setf(ios::fixed);
    cout.precision(10);
    double a, b;
    cin >> a >> b;
    cout << 4 * acos(-1) / 2 * abs(b - a) << endl;
}