#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <algorithm>

using namespace std;

int d[500];
bool cn[500][500];
int A;

int main()
{
    while (true) {
	int r;
	scanf("%d%d", &A, &r);
	if (!A && !r)
	    break;
	fill(cn[0], cn[0] + 500 * 500, false);
	
	for (int i = 0; i < r; ++i) {
	    int a, b;
	    scanf("%d%d", &a, &b);
	    d[a]++; d[b]++;
	    cn[a][b] = cn[b][a] = true;
	}
	
	int bg[3];
	int bn = 0;
	
	for (int i = 0; i < A; ++i) {
	    if (d[i] > 3) {
		if (bn == 3)
		    abort();
		bg[bn++] = i;
	    }
	}
    }

    return 0;
}