#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");
 }
 return 0;
}