#include <bits/stdc++.h>   using namespace std;   int n;   string a;   vector<pair<int, int> > v;   void input() {     cin >> a;     n = a.size();   }   void solve() {     int i;     for (i = 0; i < n; i++) {       if (a[i] !=  a ) {         v.push_back(make_pair((a[i] -  a ), i));       }     }     int sz = v.size();     if (sz == 0) {       cout << a <<   n ;       return;     }     if ((sz % 2) != 0) {       cout <<  :( n ;       return;     }     int half = (sz / 2);     for (i = 0; i < half; i++) {       if (v[i].first != v[i + half].first) {         cout <<  :( n ;         return;       }     }     int st_id = v[half].second;     for (i = st_id; i < n; i++) {       if (a[i] ==  a ) {         cout <<  :( n ;         return;       }     }     for (i = 0; i < st_id; i++) {       cout << a[i];     }     cout <<   n ;   }   int main() {     ios_base ::sync_with_stdio(false);     cin.tie(NULL);     input();     solve();     return 0;   }   