C++ :

#include <iostream>
using namespace std;
int main() {
    int n, sum = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        sum += i;
    }
    cout << sum << endl;
    while (n > 0) {
        cout << n-- << " ";
    }
    return 0;
}