#include <bits/stdc++.h>
using namespace std;
int n;
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++)
    for (int j = 0; j < n; j++) {
      dp[j][(j + i) % n][0] =
          max(dp[(j + 1) % n][(j + i) % n][0] + to[j][(j + 1) % n],
              dp[(j + i) % n][(j + 1) % n][1] + to[j][(j + i) % n]);
      dp[(j + i) % n][j][1] =
          max(dp[(j + i - 1) % n][j][1] + to[(j + i) % n][(j + i - 1) % n],
              dp[j][(j + i - 1) % n][0] + to[(j + i) % n][j]);
    }
  for (int i = 0; i < n; i++) ans = max(ans, dp[i][(i + 1) % n][1]);
  printf("%.15lf\n", ans);
  return 0;
}
