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

int main() {
    char s[101];
    scanf("%s", s);

    int n = strlen(s);

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

    for (int i = 0; i < n; i += 2) {
        char pair[1] = { s[i], s[i+1], '\0' };
        int code = atoi(pair);

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