Solucionb

#include <iostream>

using namespace std;

long long menorDivisor(long long n)
{
    for(long long i=2; i*i <= n; i++)
        if(n%i == 0)
            return i;
    return n;
}

int main()
{
    long long n, res = 0;
    cin >> n;

    if(n%2)
    {
        n -= menorDivisor(n);
        res++;
    }

    res += n/2;

    cout << res << endl;

    return 0;
}