ac

#include <iostream>
using namespace std;
int main(){
    string a, b, c;
    cin >> a;
    int len = a.size();
    for(int i = 0; i < len; i++){
        if(i % 2 == 0){
            b += a[i];
        }else{
            c += a[i];
        }
    }
    if(b > c){
        b += c;
        cout << b;
    }else{
        c += b;
        cout << c;
    }
    return 0;
}