#include <bits/stdc++.h>
using namespace std;
const int mx = 2e3 + 505;
struct node {
  double x, y;
} a[mx];
double pw(double x) { return x * x; }
double dist(node a, node b) { return sqrt(pw(a.x - b.x) + pw(a.y - b.y)); }
double f[2][mx], g[2][mx];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%lf%lf", &a[i].x, &a[i].y);
  for (int i = 1; i < n; i++)
    for (int j = 0; j < n; j++) {
      g[i % 2][j] =
          max(g[(i + 1) % 2][(j - 1 + n) % n] + dist(a[j], a[(j - 1 + n) % n]),
              f[(i + 1) % 2][(j - i + n) % n] + dist(a[j], a[(j - i + n) % n]));
      f[i % 2][j] =
          max(f[(i + 1) % 2][(j + 1) % n] + dist(a[j], a[(j + 1) % n]),
              g[(i + 1) % 2][(i + j) % n] + dist(a[j], a[(i + j) % n]));
    }
  double ans = 0;
  for (int i = 0; i < n; i++)
    ans = max(ans, max(f[(n - 1) % 2][i], g[(n - 1) % 2][i]));
  printf("%.10f\n", ans);
  return 0;
}
