#include <iostream>
    #include <string>
    #include <algorithm>
    using namespace std;
 
    int main() {
    	string str = "mamky_tvoy_ebal";
    	int num;
    	cin >> str;
    	for(char c = 'a'; c <= 'z'; c++) {
    		num = 0;
    		for(size_t i = 0; i < str.length(); i++) {
    			if(str[i] == c) {
    				num++;
    			}
    		}
    		if (num == 1) {
    			cout << c;
    		}
    	}
    	cout << endl;
    	return 0;
    }

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