#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int n, a[N];
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  int s = 0;
  for (int i = 1; i <= n; i++) s ^= a[i];
  if (n % 2 == 0) {
    if (s != 0) {
      cout << "NO\n";
      return 0;
    }
    n--;
  }
  cout << "YES\n";
  cout << n - 2 << '\n';
  for (int i = 1; i <= n - 2; i += 2)
    cout << i << ' ' << i + 1 << ' ' << i + 2 << '\n';
  for (int i = 1; i <= n - 4; i += 2)
    cout << i << ' ' << i + 1 << ' ' << n << '\n';
  return 0;
}
