#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using Int = long long; template ostream &operator<<(ostream &os, const pair &a) { return os << "(" << a.first << ", " << a.second << ")"; }; template ostream &operator<<(ostream &os, const vector &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; } template void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; } template bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; } template bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; } #define COLOR(s) ("\x1b[" s "m") template struct MaxFlow { // Watch out when using types other than int and long long. static constexpr Flow FLOW_EPS = 1e-10L; static constexpr Flow FLOW_INF = std::numeric_limits::max(); int n, m; vector ptr, nxt, zu; vector capa; explicit MaxFlow(int n_) : n(n_), m(0), ptr(n_, -1) {} void ae(int u, int v, Flow w0, Flow w1 = 0) { assert(0 <= u); assert(u < n); assert(0 <= v); assert(v < n); assert(0 <= w0); assert(0 <= w1); nxt.push_back(ptr[u]); zu.push_back(v); capa.push_back(w0); ptr[u] = m++; nxt.push_back(ptr[v]); zu.push_back(u); capa.push_back(w1); ptr[v] = m++; } vector see, lev, que; Flow augment(int u, int t, Flow limFlow) { if (u == t) return limFlow; for (int &i = see[u]; ~i; i = nxt[i]) if (capa[i] > FLOW_EPS) { const int v = zu[i]; if (lev[u] < lev[v]) { const Flow f = augment(v, t, min(limFlow, capa[i])); if (f > FLOW_EPS) { capa[i] -= f; capa[i ^ 1] += f; return f; } } } return 0; } bool bfs(int s, int t) { for (int u = 0; u < n; ++u) { see[u] = ptr[u]; lev[u] = -1; } auto head = que.begin(), tail = que.begin(); for (lev[*tail++ = s] = 0; head != tail; ) { const int u = *head++; for (int i = ptr[u]; ~i; i = nxt[i]) if (capa[i] > FLOW_EPS) { const int v = zu[i]; if (!~lev[v]) { lev[*tail++ = v] = lev[u] + 1; if (v == t) return true; } } } return false; } Flow run(int s, int t, Flow limFlow = FLOW_INF) { see.resize(n); lev.resize(n); que.resize(n); Flow flow = 0; for (; flow + FLOW_EPS < limFlow && bfs(s, t); ) { for (Flow f; (f = augment(s, t, limFlow - flow)) > FLOW_EPS; flow += f) {} } return flow; } }; //////////////////////////////////////////////////////////////////////////////// int N, M; vector A, B; int main() { for (; ~scanf("%d%d", &N, &M); ) { A.resize(M); B.resize(M); for (int i = 0; i < M; ++i) { scanf("%d%d", &A[i], &B[i]); --A[i]; --B[i]; } vector bal(N, 0); for (int i = 0; i < M; ++i) { ++bal[A[i]]; --bal[B[i]]; } MaxFlow mf(N + 2); const int src = N, snk = N + 1; for (int i = 0; i < M; ++i) { mf.ae(A[i], B[i], 1); } for (int u = 0; u < N; ++u) { if (bal[u] > 0) mf.ae(src, u, +bal[u]); if (bal[u] < 0) mf.ae(u, snk, -bal[u]); } mf.run(src, snk); vector ans; for (int i = 0; i < M; ++i) if (!mf.capa[i << 1]) { ans.push_back(i); } printf("%d %d\n", N, (int)ans.size()); for (const int i : ans) { printf("%d %d\n", A[i] + 1, B[i] + 1); } cerr<<"========"<