DetPrim

#include <iostream>
#include <cmath>

using namespace std;

//ifstream cin("maxd.in");
//ofstream cout("maxd.out");

bool Prim(int n)
{
    if(n <= 1) return false;
    else if(n <= 3) return true;
    else if(n % 2 == 0 or n % 3 == 0) return false;
    else
    {
        for(int i = 5; i * i <= n; i += 6)
        {
            if(n % i == 0 or n % (i + 2) == 0) return false;
        }
    }

    return true;
}

int main()
{
    long long a, b, nr = 0, MIN = 1e9;
    bool gasit = false;
    cin >> a >> b;

    if(a % 2 != 0)
    {
        for(int i = a; i <= b; i += 2)
        {
            int q = i;

            if(Prim(q))
            {
                gasit = true;
                if(abs((a + b) - 2 * q) < MIN)
                {
                    MIN = abs((a + b) - 2 * q);
                    nr = q;
                }
                else if(abs((a + b) - 2 * q) == MIN)
                {
                    if(q < nr) nr = q;
                }
            }
        }
    }
    else
    {
        for(int i = a + 1; i <= b; i += 2)
        {
            int q = i;

            if(Prim(q))
            {
                gasit = true;
                if(abs((a + b) - 2 * q) < MIN)
                {
                    MIN = abs((a + b) - 2 * q);
                    nr = q;
                }
                else if(abs((a + b) - 2 * q) == MIN)
                {
                    if(q < nr) nr = q;
                }
            }
        }
    }

    if(gasit) cout << nr;
    else cout << "NU EXISTA";

    return 0;
}