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

int main() {
    char input[105];
    scanf("%s", input);

    int len = strlen(input);


    if (len % 2 != 0) {
        printf("Invalid Input");
        return 0;
    }

    char result[105];
    int resIndex = 0;

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

        int num = atoi(temp);

      if ((num >= 65 && num <= 90) || (num >= 97 && num <= 122)) {
            result[resIndex++] = (char)num;
        } else {
            printf("Invalid Input");
            return 0;
        }
    }

    result[resIndex] = '\0';
    printf("%s", result);

    return 0;
}