6.c


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#include <stdio.h>


int
main()
{
	char buf[4];
	int c, n = 0;

	while ((c = fgetc(stdin)) != EOF) {
		buf[n % 4] = c;
		++n;

		if (n >= 4
				&& buf[0] != buf[1] && buf[0] != buf[2] && buf[0] != buf[3]
				&& buf[1] != buf[2] && buf[1] != buf[3] && buf[2] != buf[3])
		{
			break;
		}
	}

	if (c == EOF) {
		printf("No marker read in %d bytes\n", n);
		return 1;
	}

	printf("Marker read after %d bytes\n", n);

	return 0;
}