For problem statement at 0-999/700-799/700-709/707/problemD.txt this is a correct solution, but verifier at 0-999/700-799/700-709/707/verifierD.go ends with reference failed: exec: "refD": executable file not found in $PATH
exit status 1 can you fix the verifier?  ```go
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

type BitSet struct {
	words []uint64
	cnt   int
}

func (b *BitSet) Clone() *BitSet {
	w := make([]uint64, len(b.words))
	copy(w, b.words)
	return &BitSet{words: w, cnt: b.cnt}
}

func (b *BitSet) Set(j int) bool {
	idx := j >> 6
	bit := uint(j & 63)
	mask := uint64(1) << bit
	if (b.words[idx] & mask) == 0 {
		b.words[idx] |= mask
		b.cnt++
		return true
	}
	return false
}

func (b *BitSet) Clear(j int) bool {
	idx := j >> 6
	bit := uint(j & 63)
	mask := uint64(1) << bit
	if (b.words[idx] & mask) != 0 {
		b.words[idx] &^= mask
		b.cnt--
		return true
	}
	return false
}

func (b *BitSet) Invert(mm int) {
	for i := range b.words {
		b.words[i] = ^b.words[i]
	}
	if mm&63 != 0 {
		lastIdx := len(b.words) - 1
		mask := (uint64(1) << (mm & 63)) - 1
		b.words[lastIdx] &= mask
	}
	b.cnt = mm - b.cnt
}

type Node struct {
	sum   int
	left  *Node
	right *Node
	shelf *BitSet
}

func Update(node *Node, l, r, pos int, newShelf *BitSet) *Node {
	if l == r {
		return &Node{sum: newShelf.cnt, shelf: newShelf}
	}
	mid := (l + r) >> 1
	var left, right *Node
	if node != nil {
		left, right = node.left, node.right
	}
	if pos <= mid {
		left = Update(left, l, mid, pos, newShelf)
	} else {
		right = Update(right, mid+1, r, pos, newShelf)
	}
	sum := 0
	if left != nil {
		sum += left.sum
	}
	if right != nil {
		sum += right.sum
	}
	return &Node{sum: sum, left: left, right: right}
}

func Query(node *Node, l, r, pos int) *BitSet {
	if node == nil {
		return nil
	}
	if l == r {
		return node.shelf
	}
	mid := (l + r) >> 1
	if pos <= mid {
		return Query(node.left, l, mid, pos)
	}
	return Query(node.right, mid+1, r, pos)
}

func main() {
	reader := bufio.NewReader(os.Stdin)
	writer := bufio.NewWriter(os.Stdout)
	defer writer.Flush()

	line, _ := reader.ReadString('\n')
	line = strings.TrimSpace(line)
	parts := strings.Fields(line)
	n, _ := strconv.Atoi(parts[0])
	m, _ := strconv.Atoi(parts[1])
	q, _ := strconv.Atoi(parts[2])

	wordCount := (m + 63) / 64
	emptyShelf := &BitSet{words: make([]uint64, wordCount), cnt: 0}

	roots := make([]*Node, q+1)
	totals := make([]int, q+1)

	for op := 1; op <= q; op++ {
		line, _ = reader.ReadString('\n')
		line = strings.TrimSpace(line)
		parts = strings.Fields(line)
		typ, _ := strconv.Atoi(parts[0])

		switch typ {
		case 1:
			i, _ := strconv.Atoi(parts[1])
			j, _ := strconv.Atoi(parts[2])
			j--

			prevRoot := roots[op-1]
			oldShelf := Query(prevRoot, 1, n, i)
			if oldShelf == nil {
				oldShelf = emptyShelf
			}
			newShelf := oldShelf.Clone()
			if newShelf.Set(j) {
				roots[op] = Update(prevRoot, 1, n, i, newShelf)
				totals[op] = roots[op].sum
			} else {
				roots[op] = prevRoot
				totals[op] = totals[op-1]
			}
		case 2:
			i, _ := strconv.Atoi(parts[1])
			j, _ := strconv.Atoi(parts[2])
			j--

			prevRoot := roots[op-1]
			oldShelf := Query(prevRoot, 1, n, i)
			if oldShelf == nil {
				oldShelf = emptyShelf
			}
			newShelf := oldShelf.Clone()
			if newShelf.Clear(j) {
				roots[op] = Update(prevRoot, 1, n, i, newShelf)
				totals[op] = roots[op].sum
			} else {
				roots[op] = prevRoot
				totals[op] = totals[op-1]
			}
		case 3:
			i, _ := strconv.Atoi(parts[1])

			prevRoot := roots[op-1]
			oldShelf := Query(prevRoot, 1, n, i)
			if oldShelf == nil {
				oldShelf = emptyShelf
			}
			newShelf := oldShelf.Clone()
			newShelf.Invert(m)
			roots[op] = Update(prevRoot, 1, n, i, newShelf)
			totals[op] = roots[op].sum
		case 4:
			k, _ := strconv.Atoi(parts[1])
			roots[op] = roots[k]
			totals[op] = totals[k]
		}
		fmt.Fprintln(writer, totals[op])
	}
}
```