#include<stdio.h>
#include<string.h>
int main()
{
    char s[101];
    scanf("%s",s);
    int len=strlen(s);
    int(len %2 !=0){
        printf("Invalid input");
        return 0;
    }
    for(int i=0;i<len;i+=2){
        int num=(s[i]-'0')* 10 +(s[i+1]-'0');
        if((num >=65 && num<= 90) || (num >= 97 && num <=122)){
            printf("%c",num);
        }
        else{
            printf("Invalid input");
            return 0;
        }
    }
    return 0;
}