diff --git a/graph/bounded_mcmf.cc b/graph/bounded_mcmf.cc
index 6014a62..6679553 100644
--- a/graph/bounded_mcmf.cc
+++ b/graph/bounded_mcmf.cc
@@ -4,15 +4,30 @@ struct bounded_mcmf {
     ll sum;
     vector<ll> fl;
     vector<ll> init;
-    bounded_mcmf(int n, int m) : sum(0), n(n), m(m), S(0), T(n + 1), net(n + 1), fl(m), init(n + 1) {}
+    vector<ll> costs;
+    bounded_mcmf(int n, int m) : sum(0), n(n), m(m), S(0), T(n + 1), net(n + 1), fl(m), init(n + 1), costs(m) {}
+    // handle negative loop case
     void add_edge(int from, int to, ll low, ll high, ll cost, int edge_id = -1) {
-        if (edge_id != -1) {
-            fl[edge_id] += low;
+        if (cost < 0) {
+            __add_edge(from, to, high, high, cost, -1);
+            __add_edge(to, from, 0, high - low, -cost, edge_id);
+        } else {
+            __add_edge(from, to, low, high, cost, edge_id);
         }
+        if (edge_id != -1) {
+            costs[edge_id] = cost;
+            if (cost < 0) {
+                fl[edge_id] += high;  // RealFlow = UpperBound - Flow
+            } else {
+                fl[edge_id] += low;   // RealFlow = LowerBound + Flow
+            }
+        }
+    }
+    void __add_edge(int from, int to, ll low, ll high, ll cost, int edge_id = -1) {
         net.add_edge(from, to, high - low, cost, edge_id, -1);
         init[to] += low, init[from] -= low;
     }
-    optional<tuple<ll, ll, vector<ll>>> run(int s, int t) {
+    void prep(int s, int t) {
         for (int i = 1; i <= n; ++i) {
             if (init[i] > 0) {
                 net.add_edge(S, i, init[i], 0, -1, -1);
@@ -22,6 +37,10 @@ struct bounded_mcmf {
             }
         }
         net.add_edge(t, s, INFLL, 0, -1, -1);
+    }
+    // min-cost max-flow
+    optional<tuple<ll, ll, vector<ll>>> run_mcmf(int s, int t) {  // BUG: unchecked code
+        prep(s, t);
         if (sum != net.run(S, T).first) {
             return nullopt;
         } else {
@@ -29,7 +48,32 @@ struct bounded_mcmf {
             for (int from = 1; from <= n; ++from) {
                 for (auto&& [to, cap, flow, cost, rev, mark] : net.edges[from]) {
                     if (mark != -1) {
-                        fl[mark] = flow;
+                        if (costs[mark] < 0) {
+                            fl[mark] -= flow;
+                        } else {
+                            fl[mark] += flow;
+                        }
+                    }
+                }
+            }
+            return {{res_flow, res_cost, fl}};
+        }
+    }
+    // min-cost flow
+    optional<tuple<ll, ll, vector<ll>>> run_mcf(int s, int t) {
+        prep(s, t);
+        auto [res_flow, res_cost] = net.run(S, T);
+        if (sum != res_flow) {
+            return nullopt;
+        } else {
+            for (int from = 1; from <= n; ++from) {
+                for (auto&& [to, cap, flow, cost, rev, mark] : net.edges[from]) {
+                    if (mark != -1) {
+                        if (costs[mark] < 0) {
+                            fl[mark] -= flow;
+                        } else {
+                            fl[mark] += flow;
+                        }
                     }
                 }
             }