#include<stdio.h>

int main(void){
    char c[]="abcdefghijklmnopqrstuvwxyz",S[100];
    scanf("%s",S);
    for(int i=0;i++;){
        if(c[i]!=S[i]){
            printf("%cto%c",c[i],S[i]);
            break;
        }
    }
    return 0;
}