#include <bits/stdc++.h>   using namespace std;   int main() {     int input;     vector<int> ret;     cin >> input;     for (int i = 1; i < input; i += 2) {       ret.push_back(i + 1);       ret.push_back(i);     }     if (ret.empty() || ret.size() != input) ret = {-1};     for (auto &d : ret) {       cout << d <<    ;     }     cout << endl;     return 0;   }   