#include <bits/stdc++.h>   using namespace std;   const int N = 5e5 + 5;   int ans[N << 1];   int main() {     int n;     cin >> n;     int b1 = n + 1;     int b2 = 2 * n - 1;     int a1 = 1;     int a2 = n;     int cnt = 1;     for (int i = 1; i <= n - 1; ++i) {       if (cnt & 1)         ans[a1++] = i, ans[a2--] = i;       else         ans[b1++] = i, ans[b2--] = i;       cnt++;     }     for (int i = 1; i <= 2 * n; ++i)       if (ans[i] == 0)         cout << n <<    ;       else         cout << ans[i] <<    ;   }   