void dfs(int x) {
    vis[x] = 1;
    nivel[x] = menor[x] = cont++;
    int sons = 0;
    REP(i, graph[x].size()) {
        if(vis[graph[x][i]] == 0) {
            sons += 1;
            pai[graph[x][i]] = x;
            dfs(graph[x][i]);
            if(menor[graph[x][i]] < menor[x]) menor[x] = menor[graph[x][i]];
            if(menor[graph[x][i]] == nivel[graph[x][i]]) {
               bridges += 1
            }
        } else if(vis[graph[x][i]] == 1 && pai[x] != graph[x][i]) {
            if(nivel[graph[x][i]] < menor[x]) menor[x] = nivel[graph[x][i]];
        }
    }
    vis[x] = 2;
}