diff --git a/khj20006/202509/17 BOJ D5 Historical Research.md b/khj20006/202509/17 BOJ D5 Historical Research.md
new file mode 100644
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+++ b/khj20006/202509/17 BOJ D5 Historical Research.md	
@@ -0,0 +1,156 @@
+```java
+import java.io.*;
+import java.util.*;
+
+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);
+    }
+
+}
+
+public class Main {
+
+    static IOController io;
+
+    //
+
+    static int N, Q, bucketSize;
+    static int[] a, origin;
+    static int[][] queries;
+    static long[] seg;
+
+    public static void update(int s, int e, int i, long v, int n) {
+        if(s == e) {
+            seg[n] += v;
+            return;
+        }
+        int m = (s+e)>>1;
+        if(i <= m) update(s,m,i,v,n*2);
+        else update(m+1,e,i,v,n*2+1);
+        seg[n] = Math.max(seg[n*2], seg[n*2+1]);
+    }
+
+    public static void main(String[] args) throws Exception {
+
+        io = new IOController();
+
+        N = io.nextInt();
+        Q = io.nextInt();
+        bucketSize = (int)Math.sqrt(N);
+        a = new int[N];
+        int[][] tmp = new int[N][];
+        origin = new int[N];
+
+        for(int i=0;i<N;i++) {
+            a[i] = io.nextInt();
+            tmp[i] = new int[]{a[i], i};
+        }
+
+        Arrays.sort(tmp, (c,d) -> c[0]-d[0]);
+        int value = 0, prev = tmp[0][0];
+        origin[0] = prev;
+        for(int i=0;i<N;i++) {
+            int v = tmp[i][0], x = tmp[i][1];
+            if(prev != v) value++;
+            a[x] = value;
+            origin[value] = v;
+            prev = v;
+        }
+
+        queries = new int[Q][];
+        for(int i=0;i<Q;i++) {
+            int s = io.nextInt()-1;
+            int e = io.nextInt()-1;
+            queries[i] = new int[]{s,e,i};
+        }
+
+        Arrays.sort(queries, (c,d) -> {
+            if(c[0] / bucketSize == d[0] / bucketSize) {
+                return c[1]-d[1];
+            }
+            return c[0] / bucketSize - d[0] / bucketSize;
+        });
+
+        long[] ans = new long[Q];
+        seg = new long[524288];
+        int s = 0, e = -1;
+        for(int i=0;i<Q;i++) {
+            int ns = queries[i][0];
+            int ne = queries[i][1];
+            int idx = queries[i][2];
+
+            while(s < ns) {
+                int val = a[s];
+                int org = origin[val];
+                update(0,100001,val,-org,1);
+                s++;
+            }
+            while(ns < s) {
+                int val = a[--s];
+                int org = origin[val];
+                update(0,100001,val,org,1);
+            }
+            while(e < ne) {
+                int val = a[++e];
+                int org = origin[val];
+                update(0,100001,val,org,1);
+            }
+            while(ne < e) {
+                int val = a[e];
+                int org = origin[val];
+                update(0,100001,val,-org,1);
+                e--;
+            }
+
+            ans[idx] = seg[1];
+
+        }
+
+        for(int i=0;i<Q;i++) io.write(ans[i] + "\n");
+
+        io.close();
+
+    }
+
+}
+```