#include <bits/stdc++.h>
using namespace std;
const int iinf = 1e9 + 7;
const int oo = 0x3f3f3f3f;
const long long linf = 1ll << 60;
const double dinf = 1e60;
template <typename T>
inline void scf(T &x) {
  bool f = 0;
  x = 0;
  char c = getchar();
  while (c != '-' && (c < '0' || c > '9')) c = getchar();
  if (c == '-') f = 1, c = getchar();
  while (c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
  if (f) x = -x;
  return;
}
template <typename T1, typename T2>
void scf(T1 &x, T2 &y) {
  scf(x);
  return scf(y);
}
template <typename T1, typename T2, typename T3>
void scf(T1 &x, T2 &y, T3 &z) {
  scf(x);
  scf(y);
  return scf(z);
}
template <typename T1, typename T2, typename T3, typename T4>
void scf(T1 &x, T2 &y, T3 &z, T4 &w) {
  scf(x);
  scf(y);
  scf(z);
  return scf(w);
}
inline char mygetchar() {
  char c = getchar();
  while (c == ' ' || c == '\n') c = getchar();
  return c;
}
template <typename T>
inline bool chkmax(T &x, const T &y) {
  return y > x ? x = y, 1 : 0;
}
template <typename T>
inline bool chkmin(T &x, const T &y) {
  return y < x ? x = y, 1 : 0;
}
const int maxn = 2510;
int n;
int x[maxn], y[maxn];
double dp[maxn][maxn][2];
double D[maxn][maxn];
inline double dst(int i, int j) { return hypot(x[i] - x[j], y[i] - y[j]); }
inline void upd(double &x, double y) { x = (y + 1e-9 >= x) ? y : x; }
int main() {
  scf(n);
  for (int i = 0, _end_ = (n); i < _end_; ++i)
    for (int j = 0, _end_ = (n); j < _end_; ++j)
      for (int f = 0, _end_ = (2); f < _end_; ++f) dp[i][j][f] = -1e60;
  for (int i = 0, _end_ = (n); i < _end_; ++i)
    scf(x[i], y[i]), dp[i][i][0] = 0.;
  for (int i = 0, _end_ = (n); i < _end_; ++i)
    for (int j = 0, _end_ = (n); j < _end_; ++j) D[i][j] = dst(i, j);
  double tmp;
  for (int len = (1), _end_ = (n - 1); len <= _end_; ++len)
    for (int i = 0, _end_ = (n); i < _end_; ++i) {
      int j = (i + len - 1) % n;
      for (int f = 0, _end_ = (2); f < _end_; ++f)
        if ((tmp = dp[i][j][f]) >= -1e-9) {
          int k = f ? j : i;
          int x = (j + 1) % n;
          int y = (i - 1 + n) % n;
          upd(dp[i][x][1], tmp + D[k][x]);
          upd(dp[y][j][0], tmp + D[k][y]);
        }
    }
  double ans = -1e60;
  for (int i = 0, _end_ = (n); i < _end_; ++i)
    for (int f = 0, _end_ = (2); f < _end_; ++f) {
      int j = (i - 1 + n) % n;
      upd(ans, dp[i][j][f]);
    }
  printf("%.12f\n", ans);
  return 0;
}
