# 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;
}