#include
     
      #include
      
       #include
       
        #include
        
         using namespace std;const int N=110;int pre[N],nex[N];int z[N],y[N];int wan[N];int fa[N];int findx(int x){    return fa[x]=(x==fa[x]?x:findx(fa[x]));}int main(){    int n;    scanf("%d",&n);    int tot1=0,tot2=0,tot3=0;    for(int i=0; i<=n; ++i) fa[i]=i;    for(int  i=1; i<=n; ++i)    {        scanf("%d%d",&pre[i],&nex[i]);        int x1=findx(i),x2=findx(pre[i]),x3=findx(nex[i]);        if(x1!=x2&&x2!=0) fa[x2]=x1;        if(x1!=x3&&x3!=0) fa[x3]=x1;        if(pre[i]==0&&nex[i]==0)        {            wan[tot2++]=i;            continue;        }        if(pre[i]==0) z[tot1++]=i;        if(nex[i]==0) y[tot3++]=i;    }    bool used[120];    memset(used,0,sizeof(used));    for(int i=0; i