// a6p2 example code with no error checking
//
#include <stdio.h>
#include <string.h>
#include <ctype.h>

int hex( int c) {
  int r = 0;
  c = toupper(c);
  if( c >= '0' && c <= '9') r = c - '0'; // ok, or use isdigit()
  else if( c >= 'A' && c <= 'F') r = c - 'A' + 10; // not portable
  return r;
}

int input( unsigned char x[]) {
  char s[BUFSIZ]; 
  fgets( s, BUFSIZ, stdin);
  int len = strlen(s)/2;
  for( int i = len-1, j = 0; i >= 0; --i, j += 2)
    x[i] = 16*hex(s[j]) + hex(s[j+1]);
  return len;
}

int main( void) {
  unsigned char a[BUFSIZ]; int alen = input(a);
  for( int i = alen-1; i >= 0; --i) printf( "%02x", a[i]);
  putchar('\n');
}