func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 100005, M = 500005;   vector<int> gr[N], path, odd;   pair<int, int> ed[M];   bool us[M];   void GetEulerCircuit(int u) {     while (true) {       while (!gr[u].empty() && us[gr[u].back()]) {         gr[u].pop_back();       }       if (gr[u].empty()) {         break;       }       us[gr[u].back()] = true;       int v = u ^ ed[gr[u].back()].first ^ ed[gr[u].back()].second;       gr[u].pop_back();       GetEulerCircuit(v);     }     path.push_back(u);   }   int main() {     ios_base::sync_with_stdio(false);     cout.tie(0);     int n, m;     scanf( %d %d  , &n, &m);     for (int i = 0; i < m; i++) {       int u, v;       scanf( %d %d  , &u, &v);       ed[i] = make_pair(u, v);       gr[u].push_back(i);       gr[v].push_back(i);     }     for (int u = 1; u <= n; u++) {       if (gr[u].size() % 2) {         odd.push_back(u);       }     }     for (int i = 0; i < odd.size(); i += 2) {       int u = odd[i], v = odd[i + 1];       ed[m] = make_pair(u, v);       gr[u].push_back(m);       gr[v].push_back(m);       m++;     }     if (m % 2) {       ed[m] = make_pair(1, 1);       gr[1].push_back(m);       gr[1].push_back(m);       m++;     }     GetEulerCircuit(1);     for (int i = 0; i < m; i++) {       int u = path[i], v = path[i + 1];       if (i % 2) {         swap(u, v);       }       ed[i] = make_pair(u, v);     }     printf( %d n , m);     for (int i = 0; i < m; i++) {       int u = ed[i].first, v = ed[i].second;       printf( %d %d n , u, v);     }   }   