//ABC00DE0G00F000
//abd00e00c00
#include<bits/stdc++.h>
using namespace std;

struct TreeNode
{
    char val;
    TreeNode *left;
    TreeNode *right;

};


TreeNode* Build()
{
    char c;
    cin>>c;
    if(c=='0') return NULL;

    //先序输入
    TreeNode *t=new TreeNode;
    t->val=c;
    t->left=Build();
    t->right=Build();

    return t;
}

/*
void Preorder_print2(TreeNode *p)//先序非递归输出
{
    stack<TreeNode*> s;
    s.push(p);
    while(!s.empty())
    {
        TreeNode *t=s.top();
        s.pop();

        cout<<t->val<<' ';
        if(t->right)s.push(t->right);
        if(t->left)s.push(t->left);
    }
}

void Preorder_print(TreeNode *p)//递归先序输出
{
    if(!p) return;
    cout<<p->val;
    Preorder_print(p->left);
    Preorder_print(p->right);

}

void Inorder_print(TreeNode *p)
{
    if(!p) return;
    Inorder_print(p->left);
    cout<<p->val;
    Inorder_print(p->right);
}


void Inorder_print2(TreeNode *p)//非递归中序输出
{
    stack<TreeNode*> s;
    TreeNode *t=p;

    while(t||!s.empty())
    {
        while(t)// 把当前节点的左子节点全部压入栈
        {
            s.push(t);
            t=t->left;
        }
        // 从栈中弹出一个节点计算
        t=s.top();
        s.pop();

        cout<<t->val<<" ";
        // 让当前节点指向右子节点
        t=t->right;
    }
}

void Postorder_print(TreeNode*p)
{
    if(!p) return;
    Postorder_print(p->left);
    Postorder_print(p->right);
    cout << p->val;
}

*/

void Postorder_print2(TreeNode*p)//后序非递归遍历:
{
    stack<TreeNode*> s;
    TreeNode* t=p;
    TreeNode* prev=NULL;

    while(t||!s.empty())
    {
        while(t)// t结点是非空结点将当前节点及其左节点全部入栈
        {
            s.push(t);
            t=t->left;
        }

        // 如果栈顶没有右子节点或右子节点已经访问完
        t=s.top();
        if(!t->right||t->right==prev)
        {
            s.pop();
            cout<<t->val<<' ';
            prev=t;
            t=NULL;
        }
        else // 有右子节点且还未访问
        t=t->right;
    }

}


int main()
{
    /*
    TreeNode* root=Build();
    Preorder_print2(root);
    puts(" ");

    Inorder_print2(root);
    puts(" ");
    */
    TreeNode* root=Build();
    Postorder_print2(root);
    puts("");


    return 0;
}