#include <bits/stdc++.h>
#define rep(i,n) for(long long i=0; i<n; i++)
#define Rep(i,n) for(long long i=1; i<n; i++)
#define ll long long
#include <math.h>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <queue>
#include <set>
#include <vector>


using namespace std;
#define PI acos(-1)




int main(){
    ll N;
    cin>>N;
  
  cout<<2*N*PI<<endl;
  return 0;
}


#include <bits/stdc++.h>
#include <cassert>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define ok() puts(ok?"Yes":"No");
#define chmax(x,y) x = max(x,y)
#define chmin(x,y) x = min(x,y)
using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;
using ii = pair<int, int>;
using vvi = vector<vi>;
using vii = vector<ii>;
using gt = greater<int>;
using minq = priority_queue<int, vector<int>, gt>;
using P = pair<ll,ll>;
const ll LINF = 1e18L + 1;
const int INF = 1e9 + 1;
//clang++ -std=c++11 -stdlib=libc++ 

int main() {
  int A,B; cin >> A >>B;
  int ans = 0;
  if (A==B) ans = A+B;
  else ans = max(A,B) * 2 -1;
  cout << ans << endl;
  return 0;
}