백준 11729 c++

#include <iostream>
#include <cmath>

using namespace std;

int input(int lower, int upper);
void hanoi(int n, int from, int to, int by);

int main(void)
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int N;

	N = input(1, 20);
	cout << ((int)pow(2, N) - 1) << "\n";
	hanoi(N, 1, 3, 2);

	return 0;
}

int input(int lower, int upper)
{
	//cout << "input()" << endl;
	int A;

	while (1)
	{
		cin >> A;
		if (A >= lower && A <= upper)
		{
			break;
		}
		else
		{
			;
		}
	}

	return A;
}

void hanoi(int n, int from, int to, int by)
{
	if (n == 1)
	{
		cout << from << " " << to << "\n";
	}
	else
	{
		hanoi(n - 1, from, by, to);
		cout << from << " " << to << "\n";
		hanoi(n - 1, by, to, from);
	}

	return;
}