#include <bits/stdc++.h>
using namespace std;
inline int read() {
  register int x = 0, f = 1;
  register char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
inline void write(int x) {
  if (x < 0) x = -x, putchar('-');
  if (x > 9) write(x / 10);
  putchar(x % 10 + '0');
}
const int N = 3010;
int n;
double f[N][N][2], ans;
struct data {
  double x, y;
} a[N];
double dis(data x, data y) {
  return sqrt((x.x - y.x) * (x.x - y.x) + (x.y - y.y) * (x.y - y.y));
}
int get(int x) {
  x = (x + n) % n;
  return x;
}
int main() {
  scanf("%lld", &n);
  for (int i = 0; i < n; i++) scanf("%lf%lf", &a[i].x, &a[i].y);
  for (int l = 2; l <= n; l++) {
    for (int i = 0; i < n; i++) {
      int j = get(i + l - 1);
      f[i][j][0] = max(f[get(i + 1)][j][0] + dis(a[i], a[get(i + 1)]),
                       f[get(i + 1)][j][1] + dis(a[i], a[j]));
      f[i][j][1] = max(f[i][get(j - 1)][0] + dis(a[i], a[j]),
                       f[i][get(j - 1)][1] + dis(a[j], a[get(j - 1)]));
    }
  }
  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\n", ans);
  return 0;
}
