#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main() {
    char input[100];
    scanf("%s", input);

    int len = strlen(input);

    // Input must be even length
    if (len % 2 != 0) {
        printf("Invalid Input");
        return 0;
    }

    char output[100];
    int k = 0;

    for (int i = 0; i < len; i += 2) {
        // take two digits
        char temp[3];
        temp[0] = input[i];
        temp[1] = input[i + 1];
        temp[2] = '\0';

        // convert to integer
        int num = atoi(temp);

        // check if it's a valid alphabet (A-Z: 65-90, a-z: 97-122)
        if ((num >= 65 && num <= 90) || (num >= 97 && num <= 122)) {
            output[k++] = (char)num;
        } else {
            printf("Invalid Input");
            return 0;
        }
    }

    output[k] = '\0'; // null terminate
    printf("%s", output);

    return 0;
}