text: #include <ctype.h>
  #include <stdio.h>
  #include <stdlib.h>
  
  #define ABC 26
  
  int main( int argc, char *argv[] )
  {
      int k, c;
  
      if ( argc > 1 ) {
          k = atoi( argv[1] );
          while ( ( c = fgetc( stdin ) ) != EOF ) {
              if ( isalpha( c ) ) {
                  fputc( ( c - 'A' - k + ABC ) % ABC + ( isupper( c ) ? 'A' : 'a' ), stdout );
              } else {
                  fputc( c, stdout );
              }
          }
      }
      return 0;
  }
  