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

int main() {
	
	int C, L;
	scanf("%d %d", &C, &L);
	int *p = malloc((C + 1) * sizeof(*p)), 
		*n = malloc(C * sizeof(*n)),
		*q = malloc(C * sizeof(*q)),
		*r = malloc(C * sizeof(*r)),
		*e = malloc(2 * L * sizeof(*e)), 
		*f = malloc(2 * L * sizeof(*f));
	for (int i = 0; i < C; i++) n[i] = 0;
	for (int i = 0; i < 2 * L; i++) {
		scanf("%d", e + i);
		n[e[i]]++;
	}
	for (int i = 0, c = 0; i < C; i++) {
		p[i] = c += n[i];
	}
	p[C] = p[C - 1];
	for (int i = 0; i < L; i++) {
		int u = e[2 * i], v = e[2 * i + 1];
		f[--p[u]] = v;
		f[--p[v]] = u;
	}

	int x = -2, y = -2, z = -2, c = 0;
	for (int i = 0; i < C; i++) {
		if (!n[i]) {
			z = y; y = x; x = 0;
		}
		if (n[i] == 1) {
			r[i] = c;
			q[c++] = i;
		}
	}
	for (int h = 1, d = 0; d < c; h++) {
		for (int b = c; d < b; d++) {
			n[q[d]] = -1;
			for (int i = p[q[d]]; i < p[q[d] + 1]; i++) {
				int g = f[i];
				if (--n[g] == 1) {
					r[g] = c;
					q[c++] = g;
				}
				else if (n[g] == 0) {
					z = y; y = x; x = 2 * h - (r[g] < b ? 1 : 0);
				}
			}
		}
	}
	int m = (x + 1) / 2 + 1 + (y + 1) / 2;
	if (m > x) x = m;
	m = (y + 1) / 2 + 2 + (z + 1) / 2;
	if (m > x) x = m;
	printf("%d\n", x);
		
	return 0;
}