#pragma GCC optimize("Ofast") #pragma GCC optimize("unroll-loops") #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; } namespace MCF { using Capa = int; using Cost = Int; constexpr int MAX_N = 100'010; constexpr int MAX_M = 100'010; constexpr int QUE_SIZE = 1 << (32 - __builtin_clz(MAX_N)); constexpr int BELLMAN_FORD_NUM_ITERS = 10; constexpr int LOG_SCALING = 4; int n, m, ptr[MAX_N], cur[MAX_N], next[MAX_M << 1], zu[MAX_M << 1]; bool on[MAX_N]; int que[QUE_SIZE], qb, qe; Capa capa[MAX_M << 1], ex[MAX_N]; Cost cost[MAX_M << 1], pot[MAX_N], pot0[MAX_N]; void init(int n_) { n = n_; m = 0; memset(ptr, ~0, n * sizeof(int)); memset(ex, 0, n * sizeof(Capa)); } void ae(int u, int v, Capa c, Cost d) { d *= (n + 1); next[m] = ptr[u]; ptr[u] = m; zu[m] = v; capa[m] = c; cost[m] = d; ++m; next[m] = ptr[v]; ptr[v] = m; zu[m] = u; capa[m] = 0; cost[m] = -d; ++m; } bool bellmanFord(Cost eps) { memcpy(pot0, pot, n * sizeof(Cost)); for (int iter = 0; iter < BELLMAN_FORD_NUM_ITERS; ++iter) { bool upd = false; for (int i = 0; i < m; ++i) { if (capa[i] > 0) { const int u = zu[i ^ 1], v = zu[i]; if (pot0[v] > pot0[u] + cost[i] + eps) { pot0[v] = pot0[u] + cost[i] + eps; upd = true; } } } if (!upd) { memcpy(pot, pot0, n * sizeof(Cost)); return true; } } return false; } Cost solve() { Cost minCost = 0; for (int i = 0; i < m; i += 2) if (minCost > cost[i]) minCost = cost[i]; Cost eps = 1; for (; eps < -minCost; eps <<= LOG_SCALING) {} memset(pot, 0, n * sizeof(Cost)); for (; eps >>= LOG_SCALING; ) { if (bellmanFord(eps)) continue; for (int i = 0; i < m; i += 2) { const int u = zu[i ^ 1], v = zu[i]; const Cost d = cost[i] + pot[u] - pot[v]; if (capa[i] > 0 && d < 0) { Capa &c = capa[i]; ex[u] -= c; ex[v] += c; capa[i ^ 1] += c; c = 0; } else if (capa[i ^ 1] > 0 && -d < 0) { Capa &c = capa[i ^ 1]; ex[v] -= c; ex[u] += c; capa[i] += c; c = 0; } } memcpy(cur, ptr, n * sizeof(int)); qb = qe = 0; for (int u = 0; u < n; ++u) if (ex[u] > 0) { que[qe] = u; ++qe &= QUE_SIZE - 1; } for (; qb != qe; ) { const int u = que[qb]; ++qb &= QUE_SIZE - 1; for (int &i = cur[u]; ~i; i = next[i]) { if (capa[i] > 0) { const int v = zu[i]; if (cost[i] + pot[u] - pot[v] < 0) { const Capa c = min(ex[u], capa[i]); if (ex[v] <= 0 && ex[v] + c > 0) { que[qe] = v; ++qe &= QUE_SIZE - 1; } ex[u] -= c; ex[v] += c; capa[i] -= c; capa[i ^ 1] += c; if (ex[u] == 0) break; } } } if (ex[u] > 0) { bool relabeled = false; for (int i = ptr[u]; ~i; i = next[i]) { if (capa[i] > 0) { const Cost p = pot[zu[i]] - cost[i] - eps; if (!relabeled || pot[u] < p) { relabeled = true; pot[u] = p; } } } cur[u] = ptr[u]; que[qe] = u; ++qe &= QUE_SIZE - 1; } } } Cost totalCost = 0; for (int i = 0; i < m; i += 2) totalCost += cost[i] * capa[i ^ 1]; return totalCost / (n + 1); } } // namespace MCF 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]; } MCF::init(N + N + N + N); auto out = [&](int u) -> int { return u; }; auto in = [&](int u) -> int { return N + u; }; auto toL = [&](int u) -> int { return N + N + u; }; auto toR = [&](int u) -> int { return N + N + N + u; }; const int big = 2 * N + 10; for (int u = 0; u < N; ++u) { MCF::ae(in(u), out(u), 1, -big); MCF::ae(toL(u), in(u), 1, 0); MCF::ae(toR(u), in(u), 1, 0); // discard if (u - 1 >= 0) MCF::ae(out(u), toL(u - 1), 1, 0); if (u + 1 < N) MCF::ae(out(u), toR(u + 1), 1, 0); } for (int u = 0; u < N - 1; ++u) { MCF::ae(toL(u + 1), toL(u), N, 0); MCF::ae(toR(u), toR(u + 1), N, 0); } // use for (int i = 0; i < M; ++i) { MCF::ae(out(A[i]), in(B[i]), 1, -1); MCF::ae(out(B[i]), in(A[i]), 1, -1); } const int ans = -(MCF::solve() + N * big); cerr<<"ans = "<