import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	char[] arr = sc.next().toCharArray();
    	for (int i = 0; i < arr.length; i++) {
    	    if (arr[i] != 'a' + i) {
    	        System.out.println((char)('a' + i) + "to" + arr[i]);
    	        return;
    	    }
    	}
    }
}