#include <bits/stdc++.h>
using namespace std;
using vi = vector<long long>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vp = vector<pair<long long, long long> >;
using vvp = vector<vp>;
using vb = vector<bool>;
using vvb = vector<vb>;
const long long inf = 1001001001001001001;
const int INF = 1001001001;
const int mod = 1000000007;
const double eps = 1e-10;
template <class T>
bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
void out(T a) {
  cout << a << '\n';
}
template <class T>
void outp(T a) {
  cout << '(' << a.first << ',' << a.second << ')' << '\n';
}
template <class T>
void outvp(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++)
    cout << '(' << v[i].first << ',' << v[i].second << ')';
  cout << '\n';
}
template <class T>
void outvvp(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) outvp(v[i]);
}
template <class T>
void outv(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) {
    if (i) cout << ' ';
    cout << v[i];
  }
  cout << '\n';
}
template <class T>
void outvv(T v) {
  for (long long i = 0; i < (long long)(v.size()); i++) outv(v[i]);
}
template <class T>
bool isin(T x, T l, T r) {
  return (l) <= (x) && (x) <= (r);
}
template <class T>
void yesno(T b) {
  if (b)
    out("yes");
  else
    out("no");
}
template <class T>
void YesNo(T b) {
  if (b)
    out("Yes");
  else
    out("No");
}
template <class T>
void YESNO(T b) {
  if (b)
    out("YES");
  else
    out("NO");
}
template <class T>
void noyes(T b) {
  if (b)
    out("no");
  else
    out("yes");
}
template <class T>
void NoYes(T b) {
  if (b)
    out("No");
  else
    out("Yes");
}
template <class T>
void NOYES(T b) {
  if (b)
    out("NO");
  else
    out("YES");
}
void outs(long long a, long long b) {
  if (a >= inf - 100)
    out(b);
  else
    out(a);
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long modpow(long long a, long long b) {
  a %= mod;
  if (b == 0) return 1;
  if (b & 1) return a * modpow(a, b - 1) % mod;
  long long k = modpow(a, b / 2);
  return k * k % mod;
}
int main() {
  long long a, b, c, d, e, f, g;
  cin >> a >> b >> c >> d >> e >> f >> g;
  string s, t;
  cin >> s >> t;
  cout << fixed << setprecision(15);
  ;
  out(a * 2 * M_PI);
}
