#include<stdio.h>

#define TXT_INIT_ODD 10
#define TXT_INIT_EVEN 2
#define PGM_INIT 4
#define PPM_INIT 8

int main(int argc, char **argv)
{
   char dfa[] =
      "vZwZcZcZeZaZpZvZgZeZXZ`ZiZhZkZkZjZwZfZfZcZmZeZaZhZhZmZnZdZdZvZfZ  "
      "fZeZ`Z`ZgZqZnZgZ`ZXZ`ZaZoZoZXZXZhZhZqZtZhZhZ`ZpZsZjZXZXZhZ`ZkZuZ  "
      "jZXZhZiZbZbZlZlZhZhZbZbZxZlZfZgZdZcZ`ZaZfZfZfZdZ`Z`ZfZgZpZpZrZiZ  "
      "`Z`ZgZqZXZXZfZ`ZhZrZaZXZpZfZiZsZXZiZfZaZtZgZaZXZaZfZuZhZXZfZaZfZ  "
      "vZvZXZfZgZ`ZwZjZaZXZ`ZiZiZkZXZbZiZXZbZXZlZXZ";
   FILE *infile = stdin;
   FILE *outfile = stdout;
   char buffer[1024];
   int type, width, height, range, ptr, width1, height1;
   int size, i, c, x;

   /* Open files */
   if( argc > 1 && (argv[1][0] != '-' || argv[1][1] != '\0') )
   {
      if( (infile = fopen(argv[1], "rb")) == NULL )
         return printf("Can not open %s for reading\n", argv[1]);
   }
   if( argc > 2 && (argv[2][0] != '-' || argv[2][1] != '\0') )
   {
      if( (outfile = fopen(argv[2], "wb+")) == NULL )
         return printf("Can not open %s for writing\n", argv[2]);
   }

   /* Initialize DFA */
   for(x = ptr = 0; dfa[ptr] != '\0'; ptr += 2)
   {
      if( dfa[ptr] != ' ' )
         dfa[x++] = dfa[ptr];
   }

   /* Read header */
   size = fread(buffer, 1, 1024, infile);
   if( size > 2 &&
       buffer[0] == 'P' &&
       sscanf(buffer, "P%d %d %d %d", &type, &width, &height, &range) == 4 &&
       (type == 5 || type == 6) &&
       range == 255 )
   {
      width1 = width;
      height1 = height;
      if( argc > 3 )
      {
         /* Dropping odd pixels instead of even pixels,
            so dimensions round up instead of down.     */
         width1++;
         height1++;
      }
      fprintf(outfile, "P%d\n%d %d\n%d\n",
              type, width1 / 2, height1 / 2, range);
      ptr = type != 5 ? PPM_INIT : PGM_INIT;
      x = 3;
   }
   else
   {
      ptr = argc > 3 ? TXT_INIT_EVEN : TXT_INIT_ODD;
   }

   /* Run DFA */
   for(i = c = 0;;)
   {
      ptr *= 6;
      ptr += (argc > 3 ? 1 : 0);

      /* Execute commands at current state */
      if( dfa[ptr] & 1 )
         fputc(c, outfile);
      if( dfa[ptr] & 16 )
         x = width;
      if( dfa[ptr] & 2 )
         x--;

      /* Read input */
      if( i == size )
      {
         if( (size = fread(buffer, 1, 1024, infile)) == 0 )
            break;
         i = 0;
      }
      c = buffer[i++];

      /* Transition to next state */
      ptr += (dfa[ptr] & 8) ? (c == '\n' ? 2 : 4) :
             (dfa[ptr] & 4) ? (x != 0 ? 2 : 4) :
             2;
      ptr = dfa[ptr] - 96;
   }

   /* Cleanup */
   fclose(infile);
   fclose(outfile);
   return 0;
}