fn.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
 
int nlp[20000];
 
int main(int argc, char **argv)
{
	int rv, i, points, lines, p1, p2, bunny;
	while (1) {
		memset(nlp, 0, 20000*sizeof(int));
		rv = scanf("%d%d", &points, &lines);
		if (rv != 2) break;
		for (i=0; i<lines; i++) {
			scanf("%d%d", &p1, &p2);
			nlp[p1]++;
			nlp[p2]++;
		}
		bunny = 0;
		for (i=0; i<points; i++) {
			if (nlp[i] >= 4) bunny = 1;
		}
		printf("%s\n", bunny ? "YES" : "NO");
	}
	return 0;
}