#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
using ld = long double;
constexpr ld PI = 3.14159265359;
int main()
{
ld a,b;
cin >> a >> b;
cout << fixed << setprecision(10) << 2*PI*(abs(b-a)) << endl; 
return 0;
}