#include <cstdio>const int maxn = 30;int e[maxn][maxn];int vis[maxn][maxn];int n, m, max;void dfs(int x, int d) {if (max < d)max = d;for (int i = 0; i < n; i++)if (!vis[x][i] && e[x][i]) {vis[x][i] = vis[i][x] = 1;dfs(i, d + 1);vis[x][i] = vis[i][x] = 0;}}int main() {while (scanf("%d%d", &n, &m) && n && m) {max = 0;int a, b;for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)vis[i][j] = e[i][j] = 0;for (int i = 0; i < m; i++) {scanf("%d%d", &a, &b);e[a][b] = e[b][a] = 1;}for (int i = 0; i < m; i++)dfs(i, 0);printf("%dn", max);}return 0;}
