#include<stdio.h>
#include<string.h>
int main(){
    char a[102],b[52];int i,n=0,x;
    scanf("%101s",a);
    if(strlen(a)%2 || strspn(a,"0123456789")!=strlen(a))
    {puts("Invalid Input");return 0;}
    for(i=0;a[i];i+=2){
    {x=(a[i]-'0')*10+(a[i+1]-'0');
    if((x<65 || x>122) || (x>90 && x<97))
    {puts("Invalid Input");return 0;}
    b[n++]=x;
    }
    b[n]=0;
    puts(b);
}