#include <iostream>
using namespace std;

int LietKe(int n);
int LietKe(int n)
{
	int dem = 1;
	for (int i = 1; i < n; i++)
	{
		if (n % i == 0)
			dem = dem + 1;
		
	}
	if (dem == 2)
		return 1;
	else return 0;
}
int main()
{
	int a,i,j,b,c,min;
	cout << "Vui long nhap a:";
	cin >> a;
	for (i = a + 1;; i++)
		if (LietKe(i) == 1)
		{
			b = i - a;
			break;
		}
	for (j=a-1;j>0;j--)
		if (LietKe(j) == 1)
		{
			c = a - j;
			break;
		}
	if (b > c)
		cout << a - c;
	else if (b < c)
		cout << a + b;
	else
		cout << a-c, a+b;
	return 1;
}