#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const int N = 1e7 + 4;
int solve() {
  int n;
  scanf("%d", &n);
  int req = 0;
  int a[n + 1];
  for (int i = 1; i < n + 1; i++) scanf("%d", &a[i]), req ^= a[i];
  if (n % 2 == 0 and req != 0) {
    printf("NO\n");
    return 0;
  }
  printf("YES\n");
  vector<tuple<int, int, int>> v;
  int i = 1, j;
  for (i = 1; i + 2 <= n; i += 2) {
    j = i;
    v.push_back({i, i + 1, i + 2});
  }
  for (i = j; i - 2 >= 1; i -= 2) v.push_back({i, i - 1, i - 2});
  printf("%d\n", (int)v.size());
  for (auto it : v) printf("%d %d %d\n", get<0>(it), get<1>(it), get<2>(it));
  return 0;
}
int main() {
  int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
