```go
package main

import (
	"bufio"
	"fmt"
	"os"
)

var n int
var col []int
var adj [][]int
var res []int

func dfs(u, p int) {
	for _, v := range adj[u] {
		if v != p {
			res = append(res, v)
			col[v] ^= 1
			dfs(v, u)
			res = append(res, u)
			col[u] ^= 1
		}
	}
	if col[u] == 1 {
		if p != 0 {
			res = append(res, p)
			res = append(res, u)
			col[p] ^= 1
			col[u] ^= 1
		}
	}
}

func main() {
	sc := bufio.NewReader(os.Stdin)
	fmt.Fscan(sc, &n)
	col = make([]int, n+1)
	for i := 1; i <= n; i++ {
		var c int
		fmt.Fscan(sc, &c)
		if c == -1 {
			col[i] = 1
		} else {
			col[i] = 0
		}
	}
	adj = make([][]int, n+1)
	for i := 0; i < n-1; i++ {
		var u, v int
		fmt.Fscan(sc, &u, &v)
		adj[u] = append(adj[u], v)
		adj[v] = append(adj[v], u)
	}
	res = append(res, 1)
	col[1] ^= 1
	dfs(1, 0)
	if col[1] == 1 && len(adj[1]) > 0 {
		v := adj[1][0]
		res = append(res, v)
		res = append(res, 1)
		col[v] ^= 1
		col[1] ^= 1
	}
	fmt.Println(len(res))
	for i, x := range res {
		if i > 0 {
			fmt.Print(" ")
		}
		fmt.Print(x)
	}
	fmt.Println()
}
```