#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

int tohex(int c)

{

   if ((c >= '0') && (c <= '9')) {

        return c - '0';

   }

   if ((c >= 'a') && (c <= 'f')) {

        return c - 'a' + 10;

   }

   if ((c >= 'A') && (c <= 'F')) {

        return c - 'A' + 10;

   }

   return 0;

}

int isspace(int c)

{

   if (c <= ' ') return 1;

   if (c == '\n') return 1;

   if (c == '\t') return 1;

   if (c == ':') return 1;

   if (c == ';') return 1;

   if (c == ',') return 1;

   return 0;

}

void verify_nibble(int nibble, int current)

{

   if (nibble != 0) {

        fprintf(stderr,"count mismatch %d (nibbles=0x%x)\n",nibble,current);

        fflush(stderr);

   }

}

int main(int argc, char **argv)

{

   int c;

   int current = 0;

   int nibble = 0;

   int skip = 0;

   if (argv[1]) {

        skip = atoi(argv[1]);

   }

#define NIBBLE_COUNT 2

   while ((c=getchar()) != EOF) {

      if (isspace(c)) {

        verify_nibble(nibble,current);

        continue;

      }

      if (skip) {

        skip--;

        continue;

      }

      current = current << 4 | tohex(c);

      nibble++;

      if (nibble == NIBBLE_COUNT) {

        putchar(current);

        nibble = 0;

        current = 0;

      }

   }

   return 0;

}