#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(){
    char str[101];
    scanf("%s", str);
    int len = strlen(str);
    char result[101];
    int rindex = 0;
    for (int i = 0; i < len; i += 2){
        char temp[3] = {str[i], str[i+1], '\0'};
        int ascii = atoi(temp);
        if ((ascii >= 65 && ascii <= 90) || (ascii >= 97 && ascii <= 122)){
            result[rindex++] = (char)ascii;
        }else{
            printf("Invalid Input");
            return 0;
        }
        
    }
    result[rindex] = '\0';
    printf("%s", result);
    return 0;
}