#include <bits/stdc++.h>
using namespace std;
int n, ta, tb, tc, td;
double dp[2505][2505][2], to[2505][2505], x[2505], y[2505], ans;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%lf%lf", x + i, y + i);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      to[i][j] = sqrt(((x[i] - x[j]) * (x[i] - x[j])) +
                      ((y[i] - y[j]) * (y[i] - y[j])));
  for (int i = 1; i < n; i++) {
    ta = 0, tb = 1, tc = i - 1, td = i;
    for (int j = 0; j < n; j++) {
      dp[ta][td][0] =
          max(dp[tb][td][0] + to[ta][tb], dp[td][tb][1] + to[ta][td]);
      dp[td][ta][1] =
          max(dp[tc][ta][1] + to[td][tc], dp[ta][tc][0] + to[td][ta]);
      if (++ta == n) ta = 0;
      if (++tb == n) tb = 0;
      if (++tc == n) tc = 0;
      if (++td == n) td = 0;
    }
  }
  for (int i = 0; i < n; i++) ans = max(ans, dp[i][(i + 1) % n][1]);
  printf("%.15lf\n", ans);
  return 0;
}
