// #include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
int main()
{
    char input[101];
    scanf("%s", input);
    int len = strlen(input);
    char result[51];
    int r_index = 0;
    int invalid = 0;
    if (len == 0 || len % 2 != 0) 
    {
        printf("\nInvalid Input\n");
        return 0;
    }
    for (int i = 0; i < len; i += 2) 
    {
        if (!isdigit(input[i]) || !isdigit(input[i + 1])) 
        {
            invalid = 1;
            break;
        }
        int num = (input[i] - '0') * 10 + (input[i + 1] - '0');
        if ((num >= 65 && num <= 90) || (num >= 97 && num <= 122)) 
        {
            result[r_index++] = (char)num;
        } else {
            invalid = 1;
            break;
        }
    }
    result[r_index] = '\0';
    printf("%s\n", result);           
    if (invalid) 
    {
        printf("Invalid Input\n");    
    }

    return 0;
}