#include <proto/dos.h>

__far ULONG buffer[ 500 * 1024 / 4 ];

void main( void )
{
	BPTR f;
	int rc;
	ULONG sum = 0;
	int pos;
	int c;

	f = Open( "MicroDot", MODE_OLDFILE );
	if( !f )
		exit( 20 );

	rc = Read( f, buffer, sizeof( buffer ) ) / 4;

	for( c = 0; c < rc; c++ )
	{
		sum += buffer[ c ];
		if( buffer[ c ] == 0x7ec04e10 && buffer[ c + 2 ] == 0x1940e120 )
			pos = c + 1;
	}

	sum = -sum;

	Seek( f, pos * 4, OFFSET_BEGINNING );
	Write( f, &sum, 4 );
	Close( f );

}