#include <bits/stdc++.h>
using namespace std;
bool Primenumber(int x)
{
    if(x<2)
    {
        return false;
    }
    for(int i=2;i<=sqrt(x);i++)
    {
        if(x%i==0)
        {
            return false;
        }
    }
    return true;
}
int main()
{
    int n;
    cin>>n;
    bool flag = false;
    for(int i=2;i<=n-2;i++)
    {
        if(Primenumber(i) && Primenumber(i+2))
        {
            cout<<i<<" "<<i+2<<endl;
            flag = true;
        }
    }
    if(flag == false)
    {
        cout<<"empty";
    }
    return 0;
}
```
`

#include <iostream>
#include <vector>
using namespace std;

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

    if (n < 2) {
        cout << " empty" << endl;
        return 0;
    }

    // 使用埃拉托斯特尼筛法标记素数
    vector<bool> isPrime(n + 1, true);
    isPrime[0] = isPrime[1] = false;
    for (int i = 2; i * i <= n; ++i) {
        if (isPrime[i]) {
            for (int j = i * i; j <= n; j += i)
                isPrime[j] = false;
        }
    }

    // 收集所有素数到数组
    vector<int> primes;
    for (int i = 2; i <= n; ++i) {
        if (isPrime[i])
            primes.push_back(i);
    }

    // 寻找并输出素数对
    bool found = false;
    for (int i = 0; i < primes.size() - 1; ++i) {
        if (primes[i + 1] - primes[i] == 2) {
            cout<< primes[i] << " " << primes[i + 1] << endl;
            found = true;
        }
    }

    if (!found)
        cout << "empty" << endl;

    return 0;
}