func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 500009;   const int mod = 1000000007;   int n, m, x, y;   vector<int> v[N];   vector<bool> vis;   bool is;   void pre() { vis.assign(N, 0); }   void dfs(int ver, int par) {     vis[ver] = 1;     for (auto &it : v[ver]) {       if (it == par) continue;       if (vis[it] == 1) {         is = 1;         continue;       }       dfs(it, ver);     }   }   int32_t main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     cin.exceptions(cin.failbit);     ;     pre();     cin >> n >> m;     for (int i = 0; i < m; i++) {       cin >> x >> y;       v[x].push_back(y);       v[y].push_back(x);     }     int ans = 0;     for (int i = 1; i <= n; i++) {       if (vis[i]) continue;       is = 0;       dfs(i, -1);       ans++;       if (is) ans--;     }     cout << ans <<   n ;     return 0;   }   