Woburn Challenge 1999 Goldfinger

#include <iostream>
#include <vector>

using namespace std;

vector <bool> prost(16000,true);

void sieve()
{
    for (int i=2;i*i<=16000;i++)
    {
        if (prost[i])
        {
            for (int j=i*2;j<=16000;j+=i)
                prost[j]=false;
        }
    }
}

int main()
{
    int n;
    cin>>n;

    sieve();

    while (n!=-1)
    {
        int p=0;

        if (n%2!=0) p=1;

        for (int i=1;i<=n/2+p;i++)
            if (prost[n-i] && prost[i]) cout<<i<<" "<<n-i<<endl;
        cout<<endl;

        cin>>n;
    }
    return 0;
}