perechi

#include <bits/stdc++.h>
using namespace std;

const int NMAX = 12500000;
bool primes[NMAX];

inline void precompute()
{
    memset(primes, true, sizeof(primes));

    primes[1] = primes[0] = false;
    for (int i = 1; i * i <= NMAX; i++)
        if (primes[i])
        {
            for (int j = i * i; j <= NMAX; j += i)
                primes[j] = false;
        }
}

bool used[NMAX];
inline void solve(const int n)
{
    for (int i = 1; i < n * 2; i++)
        if (!used[i])
        {
            for (int j = i + 1; j <= n * 2; j++)
                if (!used[j])
                {
                    int sum = i * i + j * j;
                    if (primes[sum])
                    {
                        used[j] = true;
                        cout << i << ' ' << j << '\n';
                        break;
                    }
                }
        }
}

int main()
{
    freopen("perechi.in", "r", stdin);
    freopen("perechi.out", "w", stdout);
    int n;
    cin >> n;
    precompute();
    solve(n);
    return 0;
}