#include <bits/stdc++.h>
using namespace std;
void io() {
  ios::sync_with_stdio(0);
  cin.tie(0);
}
int main() {
  io();
  int n;
  cin >> n;
  int xr = 0;
  for (int i = 0, a; i < n; i++) {
    cin >> a;
    xr ^= a;
  }
  if (n % 2 == 0 && xr) {
    cout << "NO" << endl;
    return 0;
  }
  cout << "YES" << endl;
  cout << (n % 2 ? n - 2 : n - 3) << endl;
  for (int i = 1; i <= n - 2; i += 2) {
    cout << i << " " << i + 1 << " " << i + 2 << endl;
  }
  for (int i = (n % 2 ? n - 4 : n - 5); i >= 1; i -= 2) {
    cout << i << " " << i + 1 << " " << i + 2 << endl;
  }
  return 0;
}
