#include <stdio.h>
#include<algorithm>
#include<string.h>
using namespace std;
#define  ms(a,b) memset(a,b,sizeof(a))

using namespace std;
const int inf=0x3f3f3f3f;
const int maxn=5e5+5;

int ls[maxn],rs[maxn];
int ans=0,n,rt;
bool changed[maxn];
int dfs(int u)
{
    int lmin=(ls[u])?dfs(ls[u]):u;
    int rmin=(rs[u])?dfs(rs[u]):inf;
    if(lmin>rmin) changed[u]=true,ans++;
    return min(lmin,rmin);
}
int s;
void Output(int u)
{
    if(!u) return;
    if(changed[u])
    {
        Output(rs[u]);
        if(s!=n)
            printf("%d ",u),s++;
        else
        {
            printf("%d\n",u);
        }
        Output(ls[u]);
    }
    else
    {
        Output(ls[u]);
        if(s!=n)
            printf("%d ",u),s++;
        else
        {
            printf("%d\n",u);
        }
        Output(rs[u]);
    }
}
int main()
{
    scanf("%d%d",&n,&rt);
    for(int i=1; i<=n; i++)
        scanf("%d%d",&ls[i],&rs[i]);
    ms(changed,0);
    dfs(rt);
    printf("%d\n",ans);
    s=1;
    Output(rt);

    return 0;
}