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

int dehex(char 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); }

void main(int argc, char *argv[])
{ FILE *in=stdin, *out=stdout;
  char orikey[100],*key;
  int i,n;
  key=argv[1];
  i=0; orikey[0]=0;
                           /* read the argument, converting it from
                              hexadecimal into an array of bytes    */
  while (*key!=0)
  { n=dehex(*key)<<4;
    key+=1;
    orikey[i]=n;
    orikey[i+1]=0;
    if (*key==0) break;
    n|=dehex(*key);
    key+=1;
    orikey[i]=n;
    i+=1; }
  key=orikey;
                           /* read file, exclusive-oring each character
                              with the next byte of the key */
  while ((i=getc(in))>=0)
  { fputc(i^*key,out);
    *key;
    key+=1;
    if (*key==0) key=orikey; } }