#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    double a, b;
    cin >> a >> b;

    double ans = 2 * acos(-1) * (b-a);
    cout << setprecision(15);
    p(ans);
    
    return 0;
}