#include<stdio.h>
#include<ctype.h>
int hasdigit=0;
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;
}