#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
int main() 
{
    char input_string[101];
    scanf("%s",&input_string);

    int length = strlen(input_string);
    if (length % 2 != 0)
    {
        printf("Invalid input length\n");
        return 0;
    }
    char decoded_message[51]; 
    int decoded_index = 0;

    for (int i = 0; i < length; i += 2) 
    {

        if (!isdigit(input_string[i]) || !isdigit(input_string[i + 1])) {
            printf("Invalid character in input\n");
            return 0;
        }

        char pair_str[3];
        pair_str[0] = input_string[i];
        pair_str[1] = input_string[i + 1];
        pair_str[2] = '\0';

        int ascii_value = atoi(pair_str);

        if ((ascii_value >= 65 && ascii_value <= 90) || (ascii_value >= 97 && ascii_value <= 122)) {
            decoded_message[decoded_index++] = (char)ascii_value;
        } else {
            printf("Invalid input\n");
            return 0;
        }
    }

    decoded_message[decoded_index] = '\0';
    printf("%s\n", decoded_message);

    return 0;
}