#include<stdio.h>
#include<iostream>
#include<string>
using namespace std;
int main(){
string input;
int str[128] = { 0 };
while (getline(cin, input)){
for (int i = 0; i < input.length(); i++){
str[input]++;
}
int num = 0;
for (int i = 0; i < 128; i++){
if (str != 0){
num++;
}
}
while (num--){
int max = 0;
int temp_i = 0;
for (int i = 0; i < 128; i++){
if (max < str){
max = str;
temp_i = i;
}
}
str[temp_i] = 0;
cout << (char)temp_i;
}
cout << endl;
}
return 0;
}