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: Wrong Answer)

/*  ex9_1
    Y_Aizaki  */

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

#define SIZE 20

typedef struct string
{
    int size;
    int count;
    char date[SIZE];
    char *top;
}string;

void initialize_string(string *str); // stringの初期化
void print_string_queue(string *str); // 先頭から取り出す
void push(string *str, char unit); // stringへの追加
char pop(string *str); // stringからの削除・取り出し

int main(void){
    string str;
    char input[SIZE+1];
    // 標準入力を受け取る
    char *point = input;
    // inputからstrへ移す際のポインター
    char garbage;
    // popで取り出されるcharを捨てる場所

    scanf("%s", input);

    initialize_string(&str);
    // strの初期化
    
    while (*point){
        // Bだったらpop
        if (*point == 'B'){
            garbage = pop(&str);
        }
        // 0か1だったらpush
        else{
            push(&str, *point);
        }
        point++;
    }

    print_string_queue(&str);

    return 0;
}

void initialize_string(string *str){
    str->count = 0;
    str->size = SIZE;
    str->top = &(str->date[SIZE]);
}

void print_string_queue(string *str){
    char *point;

    point = &(str->date[SIZE]);

    for (int i = 0; i <= str->count; i++){
        printf("%c", *point--);
    }
    putchar('\n');
}

void push(string *str, char unit){
    if (str->count >= str->size){
       printf("Error stack overflow. (unit=%c)\n", unit);
       exit(1);
    }
    else{
        str->top--;
        *(str->top) = unit;
        str->count++;
    }
}

char pop(string *str){
    char unit = '\0';
    if (str->count < 0){
        printf("Error stack underflow.\n");
    }
    else{
        unit = *(str->top);
        str->top++;
        str->count--;
    }

    return unit;
}