스택

const fs = require('fs');
const input = fs.readFileSync('./dev/stdin').toString().trim().split('\n');
const stack = [];
const answer = [];

for (let i = 1; i <= input[0]; i++) {
  if (input[i].includes('push')) {
    stack.push(input[i].split(' ')[1]);
  } else if (input[i] === 'pop') {
    if (stack.length === 0) {
      answer.push(-1);
    } else {
      answer.push(stack.pop());
    }
  } else if (input[i] === 'size') {
    answer.push(stack.length);
  } else if (input[i] === 'empty') {
    if (stack.length === 0) {
      answer.push(1);
    } else {
      answer.push(0);
    }
  } else if (input[i] === 'top') {
    if (stack.length === 0) {
      answer.push(-1);
    } else {
      answer.push(stack[stack.length - 1]);
    }
  }
}

console.log(answer.join('\n'));

const fs = require('fs');
const input = fs.readFileSync('./dev/stdin').toString().trim().split('\n');
const K = +input.shift();
const stack = [];
let answer = 0;

for (let i = 0; i < K; i++) {
  if (input[i] !== '0') {
    stack.push(input[i]);
  } else {
    stack.pop();
  }
}

for (let i = 0; i < stack.length; i++) {
  answer += +stack[i];
}

console.log(answer);

const fs = require('fs');
const input = fs.readFileSync('./dev/stdin').toString().trim().split('\n');
const T = +input.shift();
const answer = new Array(T).fill(null);
let stack = 0;

for (let i = 0; i < T; i++) {
  stack = 0;
  const str = input[i].split('');
  for (let j = 0; j < str.length; j++) {
    if (str[j] === '(') {
      stack += 1;
    } else if (str[j] === ')' && stack === 0) {
      answer[i] = 'NO';
    } else {
      stack -= 1;
    }
  }

  if (stack === 0 && answer[i] === null) {
    answer[i] = 'YES';
  } else {
    answer[i] = 'NO';
  }
}

console.log(answer.join('\n'));

const fs = require('fs');
const input = fs.readFileSync('./dev/stdin').toString().trim().split('\n');
const filteredInput = input.filter(el => el !== '.');
const answer = new Array(filteredInput.length).fill(null);
let stack = [];

for (let i = 0; i < answer.length; i++) {
  stack = [];
  const str = filteredInput[i].split('');
  str.pop();
  for (let j = 0; j < str.length; j++) {
    if (str[j] === '[') {
      stack.push('[');
    } else if (str[j] === '(') {
      stack.push('(');
    } else if (str[j] === ']') {
      if (stack.length === 0) {
        answer[i] = 'no';
        break;
      }
      if (stack[stack.length - 1] === '[') {
        stack.pop();
      } else {
        answer[i] = 'no';
        break;
      }
    } else if (str[j] === ')') {
      if (stack.length === 0) {
        answer[i] = 'no';
        break;
      }
      if (stack[stack.length - 1] === '(') {
        stack.pop();
      } else {
        answer[i] = 'no';
        break;
      }
    }
  }

  if (answer[i] === null) {
    if (stack.length === 0) {
      answer[i] = 'yes';
    } else {
      answer[i] = 'no';
    }
  }
}

console.log(answer.join('\n'));

const fs = require('fs');
const input = fs.readFileSync('./dev/stdin').toString().trim().split('\n').map(Number);
const n = +input.shift();
const stack = [];
let answer = '';
let count = 1;
let i = 0;

while (true) {
  if (i === n) break;

  if (count <= input[i]) {
    stack.push(count);
    count++;
    answer += '+\n';
  } else {
    if (stack[stack.length - 1] !== input[i]) {
      answer = 'NO';
      break;
    }
    stack.pop();
    i++;
    answer += '-\n';
  }
}

console.log(answer.trim());