#include <bits/stdc++.h>
#define rep(a,n) for (int a = 0; a < (n); ++a)
using namespace std;
using ll = long long;
typedef pair<int,int> P;
typedef pair<ll,P> PP;
typedef vector<vector<int> > Graph;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1e18;



int main(){
    string s;
    cin >> s;
    char from,to;
    rep(i,26){
        if(s[i]-'a'!=i){
            from = 'a';
            rep(j,i)from++;
            to = s[i];
            break;
        }
    }   
    printf("%cto%c\n",from,to);
    return 0;
}