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
    shu_t */

#include <stdio.h>
#include <stdlib.h>
//1<=|s|<=10 + '\0'
#define SIZE 11

typedef struct stack{
    int size;//max size of stack
    int count;//the number of data
    char data[SIZE];//data array
    char *top;//pointer of top
}stack;

void initialize_stack(stack *stk){//initialization
    stk->count=0;
    stk->size = SIZE;
    stk->top=&(stk->data[SIZE]);//top is final element
}

void push(stack *stk,char elem){
	if(stk->count < stk->size){//prevent overflow
        stk->top--;//push top
        *(stk->top)=elem;//store data
        stk->count++;//increment
    }
}

void pop(stack *stk){
    if(stk->count > 0){//prevent underflow
        stk->top++;//pop top
        stk->count--;//decrement
    }
}

void print_stack(stack *stk){
    char *ptr;
    int i;
    ptr = stk->top;//to top pointer
    while(i<stk->count-1){//move to old data
        ptr++;
        i++;
    }
    for(i=0;i<stk->count;i++){//from old data to new data
        printf("%c",*ptr--);
    }
    printf("\n");//make a new line
}

int main(void){
    stack string;
    int i;//roop variable
    char keyboard[SIZE];//for input
    
    //input string
    scanf("%s",keyboard);
    //initialize stack
    initialize_stack(&string);
    //stack
    for(i=0;i<SIZE;i++){
        if(keyboard[i] == '0'){
            push(&string,'0');
        }
        else if(keyboard[i] == '1'){
            push(&string,'1');
        }
        else if(keyboard[i]=='B'){
            pop(&string);
        }
    }
    //output
    print_stack(&string);
    return 0;
}