diff --git a/JaeHunJang/BOJ_15961.java b/JaeHunJang/BOJ_15961.java
new file mode 100644
index 0000000..06d091d
--- /dev/null
+++ b/JaeHunJang/BOJ_15961.java
@@ -0,0 +1,69 @@
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.StringTokenizer;
+
+// 회전 초밥
+public class BOJ_15961 {
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static StringBuilder sb = new StringBuilder();
+	static StringTokenizer st;
+	static int N, d, k, c, maxCount, sushi[];
+	static Map<Integer, Integer> sushiType;
+	static boolean visited[];
+	public static void main(String[] args) throws Exception {
+		init();
+		solve();
+		print();
+	}
+	private static void print() {
+		System.out.println(sb.toString());
+	}
+	
+	private static void init() throws Exception { 
+		st = new StringTokenizer(br.readLine());
+		N = Integer.parseInt(st.nextToken()); // 접시 수
+		d = Integer.parseInt(st.nextToken()); // 초밥의 가짓수
+		k = Integer.parseInt(st.nextToken()); // 연속해서 먹는 접시의 수
+		c = Integer.parseInt(st.nextToken()); // 쿠폰 번호
+		
+		sushi = new int[N]; // 초밥 벨트에 놓인 초밥
+		for (int i = 0; i < N; i++) {
+			sushi[i] = Integer.parseInt(br.readLine());
+		}
+		
+		sushiType = new HashMap<>();
+		for (int i = 0; i < k; i++) {
+			sushiType.put(sushi[i], sushiType.getOrDefault(sushi[i], 0) + 1);
+		}
+		maxCount = sushiType.size();
+		if (sushiType.getOrDefault(c, -1) < 0) maxCount++;
+	}
+	
+	private static void solve() throws Exception {
+		slidingWindow();
+		sb.append(maxCount);
+	}
+	
+	private static void slidingWindow() {
+		int key, value;
+		for(int i = 0; i < N; i++) {
+			key = sushi[i%N]; // 내가 먹는 거에서 뺄 초밥
+			value = sushiType.get(key)-1;
+			if (value == 0) sushiType.remove((Integer)key);
+			else {
+				sushiType.put(key, value);
+			}
+			
+			key = sushi[(i+k)%N]; // 새로 넣을 초밥
+			sushiType.put(key, sushiType.getOrDefault(key, 0) + 1);
+			
+			if (sushiType.getOrDefault(c, -1) < 0) { // 쿠폰으로 받을 초밥이 없다면 +1 해줌
+				maxCount = Math.max(maxCount, sushiType.size()+1);
+			} else {
+				maxCount = Math.max(maxCount, sushiType.size());
+			}
+		}
+	}
+}
\ No newline at end of file
diff --git a/JaeHunJang/BOJ_18866.java b/JaeHunJang/BOJ_18866.java
new file mode 100644
index 0000000..e9296d3
--- /dev/null
+++ b/JaeHunJang/BOJ_18866.java
@@ -0,0 +1,33 @@
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.StringTokenizer;
+
+// 젊은 날의 생이여 / 60분
+public class BOJ_18866 {
+    static int N;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+
+        int[] u = new int[N];  // 행복도
+        int[] v = new int[N];  // 피로도
+
+        for (int i = 0; i < N; i++) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            u[i] = Integer.parseInt(st.nextToken());
+            v[i] = Integer.parseInt(st.nextToken());
+        }
+
+        int max_diff = 0;
+        int min_diff = 0;
+        for (int i = 0; i < N; i++) {
+            int diff = u[i] - v[i];  // 행복도와 피로도의 차이
+            max_diff = Math.max(max_diff, max_diff + diff);
+            min_diff = Math.min(min_diff, min_diff + diff);
+        }
+
+        int result = (max_diff - min_diff) / 2;
+        System.out.println(result);
+    }
+}