#include<iostream>
using namespace std;
int node,edge;
bool vis[30][30];
int graph[30][30];
void init(){
    for(int i=0;i<30;i++){
        for(int j=0;j<30;j++){
            vis[i][j] = false;
        }
    }
}
int dfs(int node){
    int ans = 0;
    for(int i=0;i<30;i++){
        if(graph[node][i]==1 && vis[node][i]==false){
            vis[node][i] = true;
            vis[i][node] = true;
            ans = max(1+dfs(i),ans);
            vis[node][i]==false;
            vis[i][node]==false;
        }

    }
    return ans;

}

int main(){
    while(1) {
        cin >> node >> edge;
        if(node==0 && edge==0)break;
        for (int i = 0; i < 30; i++) {
            for (int j = 0; j < 30; j++) {
                graph[i][j] = 0;
            }
        }

        for (int i = 0; i < edge; i++) {
            int x, y;
            cin >> x >> y;
            graph[x][y] = 1;
            graph[y][x] = 1;
        }
        int length = 0;
        for (int i = 0; i < node; i++) {
            init();
            length = max(dfs(i), length);
        }
        cout << length << NL;

    }



}