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)

/*  ex9_1 Stack (Keyboard)
    pandacodeb  */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE 10

//スタックの構造体(配列型)
typedef struct stack{
    int size;
    int count;
    char data[SIZE];
    char *top;
}stack;

//スタックを初期化
void init_stack(stack *stk){
    stk->count = 0;
    stk->size = SIZE;
    stk->top = &(stk->data[SIZE]);
}

//スタックに要素を入れる
void push(stack *stk, char key){
    if (stk->count >= stk->size)
        exit(1);
    else{
        stk->top--;
        *(stk->top) = key;
        stk->count++;
    }
}

//スタックを最後に入れたキーを取り出す
char pop(stack *stk){
    char latest;
    if (stk->count <= 0){
        return ' ';
    }
    else{
        latest = *(stk->top);
        stk->top++;
        stk->count--;
        return latest;
    }
}

//スタックを表示
void print_s(stack *stk){
    char *ptr;
    ptr = (stk->top)+(stk->count)-1;
    for (int i = 0; i < stk->count; i++)
        printf("%c", *ptr--);
    printf("\n");
}

int main(void){
    int i;
    char del;

    //入力用
    char* text;
    text = (char*) malloc(sizeof(char)*10);
    scanf("%s", text);

    //スタックの宣言
    stack stk;
    init_stack(&stk);

    //最後の入力キーまで
    for (i = 0; i < strlen(text); i++){
        //キーが 0 あるいは 1 の場合 -> スタックに入れる
        if (text[i] == '0' || text[i] == '1')
            push(&stk, text[i]);
        //キーが B の場合 -> スタックを最後に入れたキーを取り出す
        else if (text[i] == 'B')
            del = pop(&stk);
    }

    //出力 (スタックの底からトップまで)
    print_s(&stk);
    
    return 0;
}