Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.

using namespace std;

int main() {

    int n;cin >> n;
    int ans = 0;
    ans += (n%10)*10;
    ans += (n/10)*99;

    cout << ans;

    return 0;
}