#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 100000 + 5;
const int MAX_M = 100000 + 5;
const int INF = 0x7fffffff;
const int inf = 1000000000;
const double EPS = 1e-6;
const unsigned long long base = 123;
const long long mod = 1e4 + 7;
const double pi = 4 * atan(1.0);
int a[MAX_N];
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
  }
  int s = a[1];
  for (int i = 2; i <= n; i++) {
    s ^= a[i];
  }
  if (n % 2 == 0) {
    if (s != 0) {
      cout << "NO" << endl;
      return 0;
    }
    n--;
  }
  cout << "YES" << endl;
  cout << n - 2 << endl;
  for (int i = 1; i + 2 <= n; i += 2) {
    cout << i << ' ' << i + 1 << ' ' << i + 2 << endl;
  }
  for (int i = 1; i + 4 <= n; i += 2) {
    cout << i << ' ' << i + 1 << ' ' << n << endl;
  }
}
