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

int
get_char_int(char in)
{
    char buf[2];
    buf[0] = in;
    buf[1] = 0;
    return atoi(buf);
}

char*
decode(char *in)
{
    static char result[9];
    int idx = 0;

    if (strlen(in) != 16) {
        return NULL;
    }

    for (int i = 0; i < 15; i += 2, ++idx) {
        int first = get_char_int(in[i]);
        int second = get_char_int(in[i+1]);
        result[idx] = first * 16 + second;
    }

    result[8] = 0;

    return &result[0];
}


int
main(int argc, char **argv)
{
    char *input = "3041314232433344";
    char *result = decode(input);

    printf("keyword is: %s\n", result);

    return 0;
}