#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, const U &b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, const U &b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T1, class T2>
inline void gn(T1 &x1, T2 &x2) {
  gn(x1), gn(x2);
}
template <class T1, class T2, class T3>
inline void gn(T1 &x1, T2 &x2, T3 &x3) {
  gn(x1, x2), gn(x3);
}
template <class T1, class T2, class T3, class T4>
inline void gn(T1 &x1, T2 &x2, T3 &x3, T4 &x4) {
  gn(x1, x2), gn(x3, x4);
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T>
inline void println(T first) {
  print(first);
  putchar('\n');
}
template <class T>
inline void printsp(T first) {
  print(first);
  putchar(' ');
}
template <class T1, class T2>
inline void print(T1 x1, T2 x2) {
  printsp(x1), println(x2);
}
template <class T1, class T2, class T3>
inline void print(T1 x1, T2 x2, T3 x3) {
  printsp(x1), printsp(x2), println(x3);
}
template <class T1, class T2, class T3, class T4>
inline void print(T1 x1, T2 x2, T3 x3, T4 x4) {
  printsp(x1), printsp(x2), printsp(x3), println(x4);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = (long long)a * a % m)
    if (b & 1) ans = (long long)ans * a % m;
  return ans;
}
int a[100100];
vector<pair<pair<int, int>, int> > ans;
void rev(int first, int second, int z) {
  ans.push_back(pair<pair<int, int>, int>(pair<int, int>(first, second), z));
  a[first] ^= 1, a[second] ^= 1, a[z] ^= 1;
}
void ok() {
  puts("YES");
  println(ans.size());
  for (int i = 0; i < ans.size(); i++)
    print(ans[i].first.first, ans[i].first.second, ans[i].second);
}
int main() {
  int n;
  gn(n);
  for (int i = 1; i <= n; i++) gn(a[i]);
  for (int i = n; i >= 3; i--)
    if (a[i]) {
      if (i <= 8)
        rev(i - 2, i - 1, i);
      else if (a[i - 2]) {
        if (a[i - 1])
          rev(i - 2, i - 1, i);
        else
          rev(i - 4, i - 2, i);
      } else {
        if (a[i - 1]) {
          if (a[i - 5] && a[i - 4] && a[i - 3]) {
            rev(i - 5, i - 3, i - 1);
            rev(i - 8, i - 4, i);
          } else {
            if (i <= 12)
              rev(i - 2, i - 1, i);
            else {
              int first = i - 6, second = i - 6;
              for (int j = i - 5; j <= i - 3; j++)
                if (a[j]) {
                  first = j;
                  swap(first, second);
                }
              rev(2 * first - (i - 1), first, i - 1);
              rev(2 * second - i, second, i);
            }
          }
        } else
          rev(i - 6, i - 3, i);
      }
    }
  if (!a[1] && !a[2])
    ok();
  else if (n < 7 || n == 7 && a[2])
    puts("NO");
  else {
    if (a[1]) {
      rev(1, 4, 7);
      rev(4, 5, 6);
      rev(5, 6, 7);
    }
    if (a[2]) {
      rev(2, 5, 8);
      rev(5, 6, 7);
      rev(6, 7, 8);
    }
    ok();
  }
}
