#include <bits/stdc++.h>
#define _kiet  int main()
#define ll long long
#define str string
#define fir first
#define sec second
#define ld long double
#define pb push_back
#define MOD 100000009
#define freopen(name) if(fopen(name".INP","r")) {freopen (name".INP","r",stdin); freopen (name".OUT","w",stdout);}
#define ALL(x) (x).begin(),(x).end()
#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
using namespace std;
_kiet
{
    FAST
    ll n;
    cin >> n;
    ll x, y;
    x = (n % 100) / 10;
    y = n % 10;
    if(n < 10) cout << "-1";
    else cout << x << y << endl;
    return 0;
}

Vì các số `n` với `100 > n >= 10` vẫn có hàng chục (vẫn có 2 chữ số tận cùng), còn số `n < 10` không có đủ 2 chữ số mới in ra `-1`

$\texttt{C++}$ (Fixed)

#include <bits/stdc++.h>
#define _kiet  int main()
#define ll long long
#define str string
#define fir first
#define sec second
#define ld long double
#define pb push_back
#define MOD 100000009
#define freopen(name) if(fopen(name".INP","r")) {freopen (name".INP","r",stdin); freopen (name".OUT","w",stdout);}
#define ALL(x) (x).begin(),(x).end()
#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
using namespace std;
_kiet
{
    FAST
    ll n;
    cin >> n;
    ll x, y;
    x = (n % 100) / 10;
    y = n % 10;
    if(n < 10) cout << "-1";
    else cout << x << y << endl;
    return 0;
}