#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 10;
int a[MAXN];
void solve() {
  int n, sum = 0;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sum ^= a[i];
  }
  if (n % 2 == 0 && sum) {
    puts("NO");
    return;
  }
  puts("YES");
  if (n % 2 == 0) n--;
  printf("%d\n", n - 1);
  for (int i = 1; i <= n - 1; i += 2) printf("%d %d %d\n", i, i + 1, i + 2);
  for (int i = 1; i <= n - 1; i += 2) printf("%d %d %d\n", i, i + 1, n);
}
int main() {
  solve();
  return 0;
}
