class BigNumber {
  constructor(num) {
    this.stepN = 8;
    this.step = ~~ Math.pow(10, this.stepN);
    if (num instanceof BigNumber) {
      this.digits = num.digits.slice();
      this.trailing0 = num.trailing0;
    } else if (typeof num === 'object') {
      this.digits = num.digits || [];
      this.trailing0 = num.trailing0 || 0;
    } else {
      this.digits = [];
      this.trailing0 = 0;
      while (num) {
        this.digits.push(num % this.step);
        num = ~~ (num / this.step);
      }
    }
  }

  multiply(other) {
    if (!(other instanceof BigNumber)) {
      return this.multiplySimple(other);
    }
    let x = 0;
    const digits = [];
    const selfLength = this.digits.length;
    const otherLength = other.digits.length;
    const totalLength = selfLength + otherLength - 1;
    for (let i = 0; i < totalLength; i ++) {
      for (let j = Math.max(0, i - otherLength + 1); j < selfLength && j <= i; j ++) {
        x += this.digits[j] * other.digits[i - j];
      }
      digits.push(x % this.step);
      x = ~~ (x / this.step);
    }
    while (x) {
      digits.push(x % this.step);
      x = ~~ (x / this.step);
    }
    let trailing0 = this.trailing0 + other.trailing0;
    while (digits.length && !digits[0]) {
      digits.shift();
      trailing0 ++;
    }
    return new BigNumber({digits, trailing0});
  }

  multiplySimple(num) {
    let x = 0;
    const digits = [];
    const length = this.digits.length;
    for (let i = 0; i < length; i ++) {
      x += this.digits[i] * num;
      digits.push(x % this.step);
      x = ~~ (x / this.step);
    }
    while (x) {
      digits.push(x % this.step);
      x = ~~ (x / this.step);
    }
    let trailing0 = this.trailing0;
    while (digits.length && !digits[0]) {
      digits.shift();
      trailing0 ++;
    }
    return new BigNumber({digits, trailing0});
  }

  pow(n) {
    const midValues = {1: new BigNumber(this)};
    const keys = [1];
    for (let i = 2; i <= n; i *= 2) {
      keys.push(i);
      const midValue = new BigNumber(midValues[i >> 1]);
      midValues[i] = midValue.multiply(midValue);
    }
    let res = new BigNumber(1);
    while (n) {
      const key = +keys.pop();
      if (key <= n) {
        n -= key;
        res = res.multiply(midValues[key]);
      }
    }
    return res;
  }

  leftpad(s, n, c='0') {
    s = s.toString();
    return s.length < n ? c.repeat(n - s.length) + s : s;
  }

  toString() {
    const res = [];
    const length = this.digits.length;
    if (length) {
      res.push(this.digits[length - 1]);
      for (let i = length - 1; i --; ) {
        res.push(this.leftpad(this.digits[i], this.stepN));
      }
      res.push('0'.repeat(this.trailing0 * this.stepN));
    } else {
      res.push(0);
    }
    return res.join('');
  }
}

function test1() {
  let n = new BigNumber(65);
  console.time('calculate');
  for (let i = 0; i < 65537; i ++) n = n.multiply(65);
  console.timeEnd('calculate');
  console.time('repr');
  const s = n.toString();
  console.timeEnd('repr');
  // console.log(s);
}

function test2() {
  let n = new BigNumber(1);
  console.time('calculate');
  for (let i = 2; i <= 2000; i ++) n = n.multiply(i);
  console.timeEnd('calculate');
  console.time('repr');
  const s = n.toString();
  console.timeEnd('repr');
  // console.log(s);
}

function test3() {
  const n = new BigNumber(65);
  console.time('calculate');
  const p = n.pow(65537);
  console.timeEnd('calculate');
  console.time('repr');
  const s = p.toString();
  console.timeEnd('repr');
  // console.log(s);
}

test1();