diff --git a/graph/mcmf.cc b/graph/mcmf.cc
index ec0b030..cbb0221 100644
--- a/graph/mcmf.cc
+++ b/graph/mcmf.cc
@@ -5,6 +5,7 @@ struct mcmf {
         ll flow;
         ll cost;
         int rev;
+        bool mark;
     };
 
     vector<vector<edge>> edges;
@@ -14,9 +15,9 @@ struct mcmf {
 
     mcmf(int n) : edges(n + 1), dis(n + 1), vis(n + 1) {}
 
-    void add_edge(int from, int to, ll cap, ll cost) {
-        edges[from].push_back({ to, cap, 0, cost, int(edges[to].size()) });
-        edges[to].push_back({ from, 0, 0, -cost, int(edges[from].size() - 1)});
+    void add_edge(int from, int to, ll cap, ll cost, bool mark = false) {
+        edges[from].push_back({ to, cap, 0, cost, int(edges[to].size()), mark });
+        edges[to].push_back({ from, 0, 0, -cost, int(edges[from].size() - 1), mark });
     }
 
     bool sp(int s, int t) {