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
	suzuto	*/

#include <stdio.h>
#include <stdlib.h>
#define SIZE 10

typedef struct stack{ /*入力した文字をスタックとして重ねていくための構造体を作る*/
  int size;
  int count;
  char inp_str[SIZE];
  char *top;
}stack;

/*プロトタイプ宣言*/
void initialize_stack(stack *stack_ptr);
void push(stack *stack_ptr, char add_elem);
char pop(stack *stack_ptr);

int main(void){
  stack inp_stack, res_stack; /*変数の宣言*/
  char inp[SIZE + 1], ins;
  int i;

  initialize_stack(&inp_stack); /*inp_stackを初期化*/
  initialize_stack(&res_stack); /*res_stackを初期化*/

  scanf("%s", &inp); /*入力内容を記憶*/

  for(i = 0; i < SIZE + 1; i++){
    ins = inp[i]; /*i + 1番目の入力取り出し*/
    if(ins == '\0'){ /*末尾の識別*/
      break;
    }
    if(ins == 'B'){ /*バックスペースの時、スタックから一番上=最後に入力した文字を取り出す*/
      pop(&inp_stack);
    }
    else{
      push(&inp_stack, ins); /*文字入力の時、スタックの一番上に追加*/
    }
  }

  while (inp_stack.count > 0){ /*inp_stackの中身を全て(逆順に)res_stackに移し替える*/
    push(&res_stack, pop(&inp_stack));
  }

  while (res_stack.count > 0){ /*res_stackの中身を上から順に取り出していって答えを出力*/
    putchar(pop(&res_stack));
  }
  printf("\n"); /*改行*/
  return 0;
}

void initialize_stack(stack *stack_ptr){ /*スタックを初期化する関数*/
  stack_ptr->count = 0; /*要素の数 = 0*/
  stack_ptr->size = SIZE;
  stack_ptr->top = &(stack_ptr->inp_str[SIZE]); /*スタックの底に頂点を合わせる*/
}

void push(stack *stack_ptr, char add_elem){ /*スタックに要素を追加する関数*/
  if(stack_ptr->count >= stack_ptr->size){ /*スタックをあふれた時のエラー出力*/
    fprintf(stderr, "Error: stack overflow.\n");
    exit(1);
  }else{ /*頂点の位置を1つ上げて、その位置に要素を積む*/
    stack_ptr->top--;
    *(stack_ptr->top) = add_elem;
    stack_ptr->count++;
  }
}

char pop(stack *stack_ptr){
  char output_elem;
  if(stack_ptr->count <= 0){ /*スタックの底が尽きている時には何も取り出さない*/
    return 'B'; /*意味のない仮の出力*/
  }else{ /*一番上の要素を取り出し、頂点を一個下げる*/
    output_elem = *(stack_ptr->top);
    stack_ptr->count--;
    stack_ptr->top++;
    return output_elem;
  }
}