link
注意insert的是 res ^ val[v] ^ w

vector <ull> B;
void insert(ull x) {
    for(auto b : B)
        x = min(x, x ^ b);
    for(auto &b : B)
        b = min(b, x ^ b);
    if(x)
        B.push_back(x);
}
int head[maxn], cnt;
struct Edge {
    int to, next;
    ull w;
}edge[maxm];
void add_edge(int u, int v, ull w) {
    cnt++;
    edge[cnt].to = v;
    edge[cnt].w = w;
    edge[cnt].next = head[u];
    head[u] = cnt;
}
int vis[maxn], val[maxn];
void dfs(int u, ull res) {
    vis[u] = 1;
    val[u] = res;
    for(int i = head[u]; i; i = edge[i].next) {
        int v = edge[i].to, w = edge[i].w;
        if(!vis[v]) dfs(v, res ^ w);
        else insert(res ^ val[v] ^ w);
    }
}
void solve() {
    int n, m;
    cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        add_edge(u, v, w);
        add_edge(v, u, w);
    }
    dfs(1, 0ull);
    ull ans = val[n];
    for(auto b : B) {
        ans = max(ans, ans ^ b);
    }
    cout << ans << endl;
}