diff --git "a/khj20006/202507/28 BOJ P4 \354\206\214\352\260\200 \352\270\270\354\235\204 \352\261\264\353\204\210\352\260\204 \354\235\264\354\234\240 9.md" "b/khj20006/202507/28 BOJ P4 \354\206\214\352\260\200 \352\270\270\354\235\204 \352\261\264\353\204\210\352\260\204 \354\235\264\354\234\240 9.md"
new file mode 100644
index 00000000..85a27bf4
--- /dev/null
+++ "b/khj20006/202507/28 BOJ P4 \354\206\214\352\260\200 \352\270\270\354\235\204 \352\261\264\353\204\210\352\260\204 \354\235\264\354\234\240 9.md"	
@@ -0,0 +1,124 @@
+```java
+import java.util.*;
+import java.io.*;
+
+class IOController {
+    BufferedReader br;
+    BufferedWriter bw;
+    StringTokenizer st;
+
+    public IOController() {
+        br = new BufferedReader(new InputStreamReader(System.in));
+        bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        st = new StringTokenizer("");
+    }
+
+    String nextLine() throws Exception {
+        String line = br.readLine();
+        st = new StringTokenizer(line);
+        return line;
+    }
+
+    String nextToken() throws Exception {
+        while (!st.hasMoreTokens()) nextLine();
+        return st.nextToken();
+    }
+
+    int nextInt() throws Exception {
+        return Integer.parseInt(nextToken());
+    }
+
+    long nextLong() throws Exception {
+        return Long.parseLong(nextToken());
+    }
+
+    double nextDouble() throws Exception {
+        return Double.parseDouble(nextToken());
+    }
+
+    void close() throws Exception {
+        bw.flush();
+        bw.close();
+    }
+
+    void write(String content) throws Exception {
+        bw.write(content);
+    }
+
+}
+
+class SegTree {
+    int[] tree;
+    SegTree(int size) {
+        tree = new int[size*4];
+    }
+
+    void update(int s, int e, int i, int n) {
+        if(s == e) {
+            tree[n]++;
+            return;
+        }
+        int m = (s+e)>>1;
+        if(i <= m) update(s,m,i,n*2);
+        else update(m+1,e,i,n*2+1);
+        tree[n] = tree[n*2] + tree[n*2+1];
+    }
+
+    int find(int s, int e, int l, int r, int n) {
+        if(l>r || l>e || r<s) return 0;
+        if(l<=s && e<=r) return tree[n];
+        int m = (s+e)>>1;
+        return find(s,m,l,r,n*2) + find(m+1,e,l,r,n*2+1);
+    }
+}
+
+public class Main {
+
+    static IOController io;
+
+    //
+
+    static int N;
+    static int[] a, p;
+    static boolean[] v;
+    static SegTree seg;
+
+    public static void main(String[] args) throws Exception {
+
+        io = new IOController();
+
+        init();
+        solve();
+
+        io.close();
+
+    }
+
+    static void init() throws Exception {
+
+        N = io.nextInt();
+        a = new int[2*N+1];
+        p = new int[N+1];
+        v = new boolean[N+1];
+        for(int i=1;i<=2*N;i++) {
+            a[i] = io.nextInt();
+            p[a[i]] = i;
+        }
+        seg = new SegTree(N*2);
+
+    }
+
+    static void solve() throws Exception {
+
+        long ans = 0;
+        for(int i=1;i<=2*N;i++) if(!v[a[i]]) {
+            v[a[i]] = true;
+            ans += seg.find(1,N*2,i,p[a[i]],1);
+            seg.update(1, N*2, p[a[i]],1);
+        }
+        io.write(ans + "\n");
+
+    }
+
+}
+```