#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int x = 0;
  for (int i = 0; i < (n); i++) {
    int a;
    cin >> a;
    x ^= a;
  }
  if (!(n % 2) && x) {
    cout << "NO" << endl;
    return 0;
  } else if (!(n % 2))
    n--;
  cout << "YES" << endl << n - 1 << endl;
  for (int i = 0; i < n - 2; i += 2) {
    cout << i + 1 << " " << i + 2 << " " << i + 3;
    cout << endl;
  }
  for (int i = 0; i < n - 2; i += 2) {
    cout << i + 1 << " " << i + 2 << " " << n;
    cout << endl;
  }
}
