import sys
sys.setrecursionlimit(1000000000)
import math
import heapq
import time
from collections import deque
from collections import defaultdict
mod = 10**9+7
def solve(n):
o,e = [],[]
for i in range(1,n+1):
if i%2==0:
e.append(i)
else:
o.append(i)
return e+o+e
n = int(input())
res2 = solve(n)
print(len(res2))
print(*res2)
#include <bits/stdc++.h>
using namespace std;
#define umap unordered_map
#define cy cout << "YES" << endl
#define cn cout << "NO" << endl
#define ll long long
#define forn(i, l, r) for (int i = l; i <= r; i++)
#define forn_(i, l, r) for (int i = l; i >= r; i--)
#define debug(a) cout << #a << "=" << a << endl;
const int inf = 0x3f3f3f3f;
const int N = 2e5 + 5;
int T;
ll n;
void solve() {
cin >> n;
cout << n / 2 * 2 + (n + 1) / 2 << endl;
for (int i = 2; i <= n; i += 2) cout << i << ' ';
for (int i = 1; i <= n; i += 2) cout << i << ' ';
for (int i = 2; i <= n; i += 2) cout << i << ' ';
}
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
T = 1;
while (T--) solve();
return 0;
}
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