#include <bits/stdc++.h>
using namespace std;
int n, a[200005], sum;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i], sum ^= a[i];
  if (n % 2 == 0) {
    if (sum) {
      puts("NO");
      return 0;
    }
    n--;
  }
  puts("YES");
  printf("%d\n", n - 1);
  for (int i = 1; i <= n - 2; i += 2) printf("%d %d %d\n", i, i + 1, i + 2);
  for (int i = 1; i <= n - 2; i += 2) printf("%d %d %d\n", i, i + 1, n);
}
