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

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

    int len = strlen(str);

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

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

          int num = atoi(temp) 

        if ((num >= 65 && num <= 90) || (num >= 97 && num <= 122)) {
            printf("%c", (char)num);
        } else {
            printf("Invalid Input");
            return 0;
        }
    }

return 0;
}