#include <bits/stdc++.h>
using namespace std;
const int N = 2510;
struct Point {
  double x, y;
  Point(int x = 0, int y = 0) : x(x), y(y) {}
} p[N];
double dis(Point a, Point b) {
  return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
double f[N][N][2];
int n;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    p[i] = Point(x, y);
  }
  for (int len = 2; len <= n; len++)
    for (int l = 0; l < n; l++) {
      int r = (l + len - 1) % n;
      f[l][r][0] = max(f[(l + 1) % n][r][0] + dis(p[l], p[(l + 1) % n]),
                       f[(l + 1) % n][r][1] + dis(p[l], p[r]));
      f[l][r][1] =
          max(f[l][(r - 1 + n) % n][0] + dis(p[r], p[l]),
              f[l][(r - 1 + n) % n][1] + dis(p[r], p[(r - 1 + n) % n]));
    }
  double ans = 0;
  for (int i = 0; i < n; i++)
    ans = max(ans, max(f[i][(i + n - 1) % n][0], f[i][(i + n - 1) % n][1]));
  printf("%.10lf", ans);
  return 0;
}
