string add(string a, string b) { // take reversed, output reversed
	n = a.size
	m = b.size
	string ans(max(n, m))

	bool carry = false;
	for i = 0; i < min(n, m); i += 1 {
		ans[i] = (a[i] + b[i] + carry) % 10
		carry = (a[i] + b[i] + carry) >= 10
	}
	for i = min(n, m); i < n; i += 1 {
		ans[i] = a[i] + carry
		carry = false
	}
	for i = min(n, m); i < m; i += 1 {
		ans[i] = b[i] + carry
		carry = false
	}
	if (carry)
		ans = ans + '1'
	return ans
}

string mul_digit(string a, string digit) { // take reversed, output reversed
	n = a.size
	string ans(n)
	int carry = 0
	for i = 0; i < n; i += 1 {
		ans[i] = (a[i] * digit + carry) % 10
		carry = (a[i] * digit + carry) / 10
	}
	if carry != 0 {
		ans = ans + carry
	}
	return ans
}

string mul(string a, string b) { // take reversed, output reversed
	n = a.size
	m = b.size
	string ans = "0"
	for i = 0; i < n; i += 1 {
		string c = mul_digit(a, b[i])
		ans = add(ans, ('0'*i) + c)
	}
	return ans
}

string main(string a, string b) {
	reverse(a)
	reverse(b)
	return reverse(mul(a, b))
}