func_code_string: #include <bits/stdc++.h>   using namespace std;   struct data {     int to, head;   } e[750000 * 2];   stack<int> s;   vector<int> cir[750000];   int n, m, len, head[750000], dfn[750000], low[750000], cnt, num, p[750000],       binv[750000], d[750000];   int ans, tot;   long long mm;   int mul(int a, int b) {     int ans = 1;     while (b) {       if (b & 1) ans = 1ll * ans * a % 1000000007;       a = 1ll * a * a % 1000000007;       b >>= 1;     }     return ans;   }   void dfs(int lab, int fa) {     dfn[lab] = low[lab] = ++num;     s.push(lab);     for (int i = head[lab]; i; i = e[i].head) {       if (!dfn[e[i].to]) {         dfs(e[i].to, lab);         low[lab] = min(low[lab], low[e[i].to]);         if (low[e[i].to] == dfn[lab]) {           cnt++;           int m1;           do {             m1 = s.top();             s.pop();             if (dfn[lab] == low[m1]) cir[cnt].push_back(m1);           } while (m1 != e[i].to);           cir[cnt].push_back(lab);           m1 = cir[cnt].size();           for (auto j : cir[cnt]) p[j] = (1ll * p[j] + binv[m1]) % 1000000007;           tot = (1ll * tot + binv[m1]) % 1000000007;         }       }       if (e[i].to != fa) low[lab] = min(low[lab], dfn[e[i].to]);     }   }   void add(int u, int v) {     e[++len].to = v;     e[len].head = head[u];     head[u] = len;   }   int main() {     binv[0] = 1;     binv[1] = mul(2, 1000000007 - 2);     int u, v, m1, m2, m3;     scanf( %d%d , &n, &m);     for (int i = 1; i <= m; i++) {       scanf( %d%d , &u, &v);       add(u, v);       add(v, u);       d[u]++;       d[v]++;     }     m1 = max(n, 10);     for (int i = 2; i <= m1; i++)       binv[i] = 1ll * binv[1] * binv[i - 1] % 1000000007;     ans = 1ll * n * (n + 1) % 1000000007 * binv[2] % 1000000007;     ans = (ans + 1ll * m * binv[2]) % 1000000007;     dfs(1, 0);     for (int i = 1; i <= n; i++) {       ans = (ans - 2ll * d[i] * binv[2]) % 1000000007;       ans = (ans - 2ll * (m - d[i]) * binv[3]) % 1000000007;       ans = (ans + 2ll * p[i]) % 1000000007;       ans = (ans + 2ll * (tot - p[i]) * binv[1]) % 1000000007;       for (int j = head[i]; j; j = e[j].head) {         if (e[j].to < i) continue;         ans = (ans + (1ll * d[i] + d[e[j].to] - 3 + m) * binv[4]) % 1000000007;       }     }     ans = (1ll * ans + tot) % 1000000007;     for (int i = 1; i <= cnt; i++) {       m1 = 0;       m2 = cir[i].size(), m3 = 0;       for (auto j : cir[i]) {         m1 = (1ll * m1 + p[j] - binv[m2]) % 1000000007;         ans = (ans + 1ll * (p[j] - binv[m2]) * binv[m2] % 1000000007 * 2) %               1000000007;         m3 = (1ll * m3 + d[j] - 2) % 1000000007;         ans = (ans - 2ll * binv[m2 + 1] * (d[j] - 2)) % 1000000007;       }       m1 = (1ll * m1 + binv[m2]) % 1000000007;       ans = (ans + 1ll * (tot - m1) * binv[m2]) % 1000000007;       ans = (ans - 2ll * m2 * binv[m2]) % 1000000007;       ans = (ans - 2ll * (m - m3 - m2) * binv[m2 + 2]) % 1000000007;     }     m1 = (1ll * n * binv[1] - 1ll * m * binv[2] + 1ll * tot) % 1000000007;     ans = ((ans - 1ll * m1 * m1) % 1000000007 + 1000000007) % 1000000007;     printf( %d n , ans);   }   