#include<stdio.h>
void reverse(){
    char ch;
    if(scanf("%c",&ch)!=1)
    return;
    if(ch=='\n')
    return ;
    if(ch>='0'&&ch<='9')
    hasdigit=1;

reverse()
if(!hasdigit)
printf("%c",ch);
}
int main(){
    reverse();
    if(hasdigit){
        printf("Invalid input");
    }
}