#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin >> s;
    char ch = 'a';
    string out = "to";
    for(int i=0;i<26;i++) {
        if(s[i] == ch) ch++;
        else {
            out = ch + out;
            out += s[i];
            break;
        }
    }

    cout << out << '\n';

    return 0;
}