B - Primes

#include<bits/stdc++.h>
using namespace std;
int prime[300000],nprime;
int mark[10000007];
void sieve(int n)
{
    int i,j,limit=sqrt(n)+2;
    mark[1]=1;
    prime[nprime++]=2;
    for(i=4; i<=n; i+=2)mark[i]=1;
    for(i=3; i<=n; i+=2)
    {
        if(!mark[i])
        {
            prime[nprime++]=i;
            if(i<=limit)
            {
                for(j=i*i; j<=n; j+=i*2)
                {
                    mark[j]=1;
                }
            }
        }
    }
}
int main()
{
    int n;
    cin>>n;
    sieve(n);
    for(int i=0,j=nprime-2; i<(nprime-1)/2 && j>=(nprime-1)/2; i++,j--)
    {
        if(prime[i]+prime[j]==n)
        {
            cout<<prime[i]<<' '<<prime[j]<<endl;
            return 0;
        }
    }
    cout<<-1<<endl;
    return 0;
}