#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;

int main() {
    double a, b;
    cin >> a >> b;

    printf("%.8f\n", (b - a) * atan(1) * 4 * 2);

    return 0;
}