#include <stdint.h>
#include <stdbool.h>

#define RSYNC_WIN 4096

struct rsync_state {
	uint64_t n;			/* number of elements in the window */
	uint64_t sum;			/* current sum */
	unsigned char win[RSYNC_WIN];	/* window elements */
};

static inline
bool rsync_next(struct rsync_state *s, unsigned char c)
{
	if (s->n < RSYNC_WIN) {		/* not enough elements */
		s->sum += c;		/* update the sum */
		s->win[s->n++] = c;	/* remember the element */
		return false;		/* no match */
	}
	int i = s->n++ % RSYNC_WIN;	/* wrap up */
	s->sum -= s->win[i];		/* move the window on */
	s->sum += c;
	s->win[i] = c;
	if (s->sum % RSYNC_WIN == 0) {	/* match */
		s->n = 0;		/* reset */
		s->sum = 0;
		return true;
	}
	return false;
}

#include <stdio.h>

int main()
{
	struct rsync_state rs = { 0, 0 };
	int c;
	while ((c = getc(stdin)) != EOF)
		if (rsync_next(&rs, c))
			printf("sync at %ld\n", ftell(stdin));
	return 0;
}