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

int main() {
    char input[101];  
    scanf("%100s", input);

    int length = strlen(input);

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

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

        int num = atoi(pair);

        char ch = (char)num;


        if (!isalpha(ch)) {
            printf("Invalid Input\n");
            return 0;
        }

        printf("%c", ch);
    }

    printf("\n");
    return 0;
}