백준 5597 c++

#include <iostream>
using namespace std;

int main(void)
{
	int arr[30] = {};
	int n;

	for (int i = 0; i < 28; i++)
	{
		cin >> n;
		if (n >= 1 && n <= 30)
		{
			arr[n-1] = 1;
		}
		else
		{
			i--;
		}
	}
	for (int i = 0; i < 30; i++)
	{
		if (arr[i] != 1)
		{
			cout << i + 1 << endl;
		}
		else
		{
			;
		}
	}


	return 0;
}