#include<stdio.h>

int main()
{
    char *org="abcdefghijklmnopqrstuvwxyz";
    char c[26];
    int i;
    scanf("%s",c);
    for(i = 0;i<26;i++){
        if(org[i]!=c[i]){
            break;
        }
    }
    printf("%cto%c",org[i],c[i]);
}