#include <bits/stdc++.h>
template <class T>
inline void read(T &x) {
  x = 0;
  int f = 0;
  char ch = getchar();
  while (!isdigit(ch)) {
    f |= ch == '-';
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = (x << 1) + (x << 3) + (ch ^ 48);
    ch = getchar();
  }
  x = f ? -x : x;
  return;
}
int a[100010];
int n, s;
int main() {
  read(n);
  for (int i = 1; i <= n; ++i) read(a[i]), s ^= a[i];
  if (!(n & 1)) {
    --n;
    if (s) {
      puts("NO");
      return 0;
    }
  }
  printf("YES\n%d\n", n - 2);
  for (int i = 1; i + 2 <= n; i += 2) printf("%d %d %d\n", i, i + 1, i + 2);
  for (int i = 1; i + 4 <= n; i += 2) printf("%d %d %d\n", i, i + 1, n);
  return 0;
}
