diff --git "a/\354\265\234\354\232\260\354\204\235/\352\260\200\354\236\245 \352\270\264 \355\214\260\353\246\260\353\223\234\353\241\254.md" "b/\354\265\234\354\232\260\354\204\235/\352\260\200\354\236\245 \352\270\264 \355\214\260\353\246\260\353\223\234\353\241\254.md"
new file mode 100644
index 0000000..48cd449
--- /dev/null
+++ "b/\354\265\234\354\232\260\354\204\235/\352\260\200\354\236\245 \352\270\264 \355\214\260\353\246\260\353\223\234\353\241\254.md"	
@@ -0,0 +1,50 @@
+# 가장 긴 팰린드롬
+
+```kotlin
+import kotlin.math.*
+
+class Solution {
+    fun solution(s: String): Int {
+        var answer = 0
+ 
+        for ((i, c) in s.withIndex()) {
+            answer = max(answer, palindrome(s, i, c))
+        }
+
+        return answer
+    }
+    
+    fun palindrome(s: String, i: Int, c: Char): Int {
+        var t = 1
+        
+        var twinLength = 1
+        while (0 <= i - t && i + t < s.length && s[i - t] == s[i + t]) {
+            t += 1
+            twinLength += 2
+        }
+        
+        t = 1
+        var rightLength = 1
+        while (i + t < s.length && s[i + t] == c) {
+            t += 1
+            rightLength += 1
+        }
+        
+        var result = max(twinLength, rightLength)
+
+        var twinLength2 = 2
+        if (i + t < s.length && s[i + 1] == c) {
+            t = 1
+            var l_i = i
+            var r_i = i + 1
+            while (0 <= l_i - t && r_i + t < s.length && s[l_i - t] == s[r_i + t]) {
+                t += 1
+                twinLength2 += 2
+            }
+            result = max(result, twinLength2)
+        }
+        
+        return result
+    }
+}
+```
\ No newline at end of file
diff --git "a/\354\265\234\354\232\260\354\204\235/\353\213\244\353\213\250\352\263\204 \354\271\253\354\206\224 \355\214\220\353\247\244.md" "b/\354\265\234\354\232\260\354\204\235/\353\213\244\353\213\250\352\263\204 \354\271\253\354\206\224 \355\214\220\353\247\244.md"
new file mode 100644
index 0000000..015ef15
--- /dev/null
+++ "b/\354\265\234\354\232\260\354\204\235/\353\213\244\353\213\250\352\263\204 \354\271\253\354\206\224 \355\214\220\353\247\244.md"	
@@ -0,0 +1,51 @@
+# 다단계 칫솔 판매
+
+```kotlin
+class Solution {
+    fun solution(enroll: Array<String>, referral: Array<String>, seller: Array<String>, amount: IntArray): IntArray {
+        var answer: IntArray = intArrayOf()
+        
+        val employees = mutableListOf<Employee>()
+        
+        for (i in 0 until enroll.size) {
+            val referralEmployee = employees.find { it.name == referral[i] }
+            if (referralEmployee == null) {
+                employees.add(Employee(enroll[i], null))
+                continue
+            }
+            employees.add(Employee(enroll[i], referralEmployee))
+        }
+        
+        for (i in 0 until seller.size) {
+            val employee = employees.find { it.name == seller[i] }
+            employee!!.sell(amount[i] * 100)
+        }
+        
+        return employees.map { it.profit }.toIntArray()
+    }
+}
+
+class Employee(
+    val name: String,
+    val referralEmployee: Employee?,
+    var profit: Int = 0
+) {
+    
+    fun sell(profit: Int) {
+        val interest = profit / 10
+
+        if (interest == 0) {
+            this.profit += profit
+            return
+        }
+
+        this.profit += profit - interest
+        
+        if (referralEmployee != null) {
+            referralEmployee.sell(interest)
+        }
+    }
+}
+
+
+```
\ No newline at end of file