Problem:
Score : 200 points

Problem Statement

Sig has built his own keyboard. Designed for ultimate simplicity, this keyboard only has 3 keys on it: the 0 key, the 1 key and the backspace key.

To begin with, he is using a plain text editor with this keyboard. This editor always displays one string (possibly empty). Just after the editor is launched, this string is empty. When each key on the keyboard is pressed, the following changes occur to the string:

The 0 key: a letter 0 will be inserted to the right of the string.

The 1 key: a letter 1 will be inserted to the right of the string.

The backspace key: if the string is empty, nothing happens. Otherwise, the rightmost letter of the string is deleted.

Sig has launched the editor, and pressed these keys several times. You are given a string s, which is a record of his keystrokes in order. In this string, the letter 0 stands for the 0 key, the letter 1 stands for the 1 key and the letter B stands for the backspace key. What string is displayed in the editor now?

Constraints

1 ≦ |s| ≦ 10 (|s| denotes the length of s)

s consists of the letters 0, 1 and B.

The correct answer is not an empty string.

Input

The input is given from Standard Input in the following format:

s

Output

Print the string displayed in the editor in the end.

Sample Input 1

01B0

Sample Output 1

00

Each time the key is pressed, the string in the editor will change as follows: 0, 01, 0, 00.

Sample Input 2

0BB1

Sample Output 2

1

Each time the key is pressed, the string in the editor will change as follows: 0, (empty), (empty), 1.

Solution in C (GCC 9.2.1) (judge verdict: Accepted)

/* ex 9_1 ABC 043 B
   nk777 */
 
#include<stdio.h>
#include <stdlib.h>
//スタックに格納するデータの最大数
#define SIZE 100

//スタックの定義
typedef struct stack{
    int size;
    int count;
    char data[SIZE];
    char *top;
} stack;

//スタックの初期化
void initialize_stack(stack *stk){
    // 要素数を0にする
    stk->count = 0;
    // スタックの大きさをSIZEにする
    stk->size = SIZE;
    // topを配列の末尾にする
    stk->top = &(stk->data[SIZE]);
}

//データの追加
void push(stack *stk, char elem){
    if(stk->count >= stk->size){
        // オーバーフローするとき
        exit(1);
    }
    else{
        // 配列の番号が若いほどデータが新しい
        stk->top--;
        *(stk->top) = elem;
        stk->count++;
    }
}

//データの取り出し(削除)
char pop(stack *stk){
    char latest;
    if(stk->count <= 0){
        // アンダーフローするとき
        exit(1);
    }
    else{
        latest = *(stk->top);
        stk->top++;
        stk->count--;
        return latest;
    }
}

// スタックの中身を古い方から印刷
void print_stack(stack *stk){
    for (int i = 0; i < stk->count; i++)
    {
        // 配列の後ろから出力
        printf("%c", stk->data[SIZE - i - 1]);
    }
    printf("\n");
} 

int main(void){
    // 表示する文字列を格納するスタックstk
    stack stk;
    // カウンタi
    int i = 0;
    // 読み取った文字列を一時的に格納するword
    char word[10];
    //スタックを初期化（ポインタ渡しで関数にわたすこと）
    initialize_stack(&stk);
    //入力されたデータをスタックに追加
    scanf("%s", word);
    while (word[i] != '\0')
    {
        if (word[i] == 'B')
        {
            if (stk.count > 0)
            {
                // スタックか空じゃないときだけpop
                pop(&stk);
            }
        }
        else
        {
            // 0と1のときは追加
            push(&stk, word[i]);
        }
        i++;
    }
    // 結果の出力
    print_stack(&stk);
    return 0;
}