保证AC

#include <iostream>
using namespace std;
int main(){
    int i, d;
    cin >> i;
    d = 2;
    for (int b = 0; b < i; ++b){
        cout << d << " ";
        d -= 1;
        b ++;
        if (b >= i){
            break;
        }
        cout << d << " ";
        d += 3;
    }
}