#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #if __has_include() #include using namespace atcoder; #endif #if __has_include() #include using cpp_int=boost::multiprecision::cpp_int; #endif #if __has_include() #include templateusing cpp_float=boost::multiprecision::number>; templateusing cpp_double=boost::multiprecision::number>; #endif using namespace std; using ll=long long; #define read(x) cin>>(x); #define readll(x) ll (x);cin>>(x); #define readS(x) string (x);cin>>(x); #define readvll(x,N) vector (x)((N));for(int i=0;i<(N);i++){cin>>(x)[i];} #define rep(i,N) for(ll (i)=0;(i)<(N);(i)++) #define rep2d(i,j,H,W) for(ll (i)=0;(i)<(H);(i)++)for(ll (j)=0;(j)<(W);j++) #define is_in(x,y) (0<=(x) && (x) inline void erase_duplicate(vector& A){sort(A.begin(),A.end());A.erase(unique(A.begin(),A.end()),A.end());} inline ll powll(ll x,ll n){ll r=1;while(n>0){if(n&1){r*=x;};x*=x;n>>=1;};return r;} // https://ei1333.github.io/library/graph/flow/gabow-edmonds.hpp.html // https://qiita.com/Kutimoti_T/items/5b579773e0a24d650bdf /** * @brief Gabow Edmonds(一般グラフの最大マッチング) * @docs docs/gabow-edmonds.md */ struct GabowEdmonds { struct edge { int to, idx; }; vector< vector< edge > > g; vector< pair< int, int > > edges; vector< int > mate, label, first; queue< int > que; GabowEdmonds(int n) : g(n + 1), mate(n + 1), label(n + 1, -1), first(n + 1) {} void add_edge(int u, int v) { ++u, ++v; g[u].push_back(edge{v, (int) (edges.size() + g.size())}); g[v].push_back(edge{u, (int) (edges.size() + g.size())}); edges.emplace_back(u, v); } int find(int x) { if(label[first[x]] < 0) return first[x]; first[x] = find(first[x]); return first[x]; } void rematch(int v, int w) { int t = mate[v]; mate[v] = w; if(mate[t] != v) return; if(label[v] < (int)g.size()) { mate[t] = label[v]; rematch(label[v], t); } else { int x = edges[label[v] - g.size()].first; int y = edges[label[v] - g.size()].second; rematch(x, y); rematch(y, x); } } void assign_label(int x, int y, int num) { int r = find(x); int s = find(y); int join = 0; if(r == s) return; label[r] = -num; label[s] = -num; while(true) { if(s != 0) swap(r, s); r = find(label[mate[r]]); if(label[r] == -num) { join = r; break; } label[r] = -num; } int v = first[x]; while(v != join) { que.push(v); label[v] = num; first[v] = join; v = first[label[mate[v]]]; } v = first[y]; while(v != join) { que.push(v); label[v] = num; first[v] = join; v = first[label[mate[v]]]; } } bool augment_check(int u) { que = queue< int >(); first[u] = 0; label[u] = 0; que.push(u); while(!que.empty()) { int x = que.front(); que.pop(); for(auto e : g[x]) { int y = e.to; if(mate[y] == 0 && y != u) { mate[y] = x; rematch(x, y); return true; } else if(label[y] >= 0) { assign_label(x, y, e.idx); } else if(label[mate[y]] < 0) { label[mate[y]] = x; first[mate[y]] = y; que.push(mate[y]); } } } return false; } vector< pair< int, int > > max_matching() { for(int i = 1; i < (int)g.size(); i++) { if(mate[i] != 0) continue; if(augment_check(i)) label.assign(g.size(), -1); } vector< pair< int, int > > ret; for(int i = 1; i < (int)g.size(); i++) { if(i < mate[i]) ret.emplace_back(i - 1, mate[i] - 1); } return ret; } }; inline ll conv(ll x,ll y){ return 10'000'000LL*x+y; } int main(){ ll N,M; cin>>N>>M; GabowEdmonds GE(N); unordered_map index; for(ll i=0;i>u>>v; u--;v--; ll vmin=min(u,v),vmax=max(u,v); GE.add_edge(vmin,vmax); index[conv(vmin,vmax)]=i+1; } auto res=GE.max_matching(); cout<