func_code_string: #include <bits/stdc++.h>   #pragma GCC optimize( O3 )   #pragma GCC target( sse4 )   using namespace std;   template <class T>   bool ckmin(T& a, const T& b) {     return b < a ? a = b, 1 : 0;   }   template <class T>   bool ckmax(T& a, const T& b) {     return a < b ? a = b, 1 : 0;   }   mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());   const int MOD = 1000000007;   const char nl =   n ;   const int MX = 41;   int in = 18, out;   int N;   vector<vector<int> > graph(MX);   int cc = 0;   bool bi = true;   void ff() {     int col[N];     for (int i = 0; i < (N); i++) col[i] = -1;     for (int r = 0; r < (N); r++) {       if (col[r] != -1) continue;       col[r] = 0;       queue<int> q;       q.push(r);       while (!q.empty()) {         int cur = q.front();         q.pop();         for (auto& a : graph[cur]) {           if (col[a] != -1) {             if (col[a] == col[cur]) bi = false;           } else {             col[a] = 1 - col[cur];             q.push(a);           }         }       }       cc++;     }   }   long long cis() {     long long mask[N];     for (int i = 0; i < (N); i++) {       mask[i] = 1ll << N;       mask[i]--;       for (auto& a : graph[i]) {         mask[i] -= 1ll << a;       }     }     long long dp[(1ll << out)];     for (int m = 0; m < ((1ll << out)); m++) {       long long cm = 1ll << N;       cm--;       for (int i = 0; i < (out); i++) {         if (m & (1ll << i)) cm &= mask[i + in];       }       bool good = true;       for (int i = 0; i < (out); i++) {         if ((m & (1ll << i)) && !(cm & (1ll << (i + in)))) good = false;       }       dp[m] = 0;       if (good) dp[m] = 1ll;     }     for (int i = 0; i < (out); i++)       for (int m = 0; m < ((1ll << out)); m++)         if (m & (1ll << i)) dp[m] += dp[m ^ (1ll << i)];     long long ans = 0;     for (int m = 0; m < ((1ll << in)); m++) {       long long cm = 1ll << N;       cm--;       for (int i = 0; i < (in); i++) {         if (m & (1ll << i)) cm &= mask[i];       }       bool good = true;       for (int i = 0; i < (in); i++) {         if ((m & (1ll << i)) && !(cm & (1ll << (i)))) good = false;       }       if (good) {         ans += dp[cm >> in];       }     }     return ans;   }   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cin >> N;     int M;     cin >> M;     vector<pair<int, int> > edges;     bool found[N];     for (int i = 0; i < (N); i++) found[i] = false;     for (int i = 0; i < (M); i++) {       int A, B;       cin >> A >> B;       A--;       B--;       edges.push_back({A, B});       found[A] = true;       found[B] = true;     }     int ind[N];     int nxt = 0;     long long mul = 1;     for (int i = 0; i < (N); i++) {       if (found[i]) {         ind[i] = nxt;         nxt++;       } else {         mul *= 2;       }     }     N = nxt;     ckmin(in, N);     out = N - in;     if (M == 0) {       cout << 0 << nl;       return 0;     }     for (int i = 0; i < (M); i++) {       int A = edges[i].first;       int B = edges[i].second;       A = ind[A];       B = ind[B];       graph[A].push_back(B);       graph[B].push_back(A);     }     ff();     long long is = cis();     long long ans = (1ll << N);     ans -= 2 * is;     if (!bi) ans -= (1ll << cc);     ans += 2;     cout << ans * mul << nl;     return 0;   }   