diff --git a/CMakeLists.txt b/CMakeLists.txt
index e212797..d57756f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -25,4 +25,5 @@ add_executable(Playground
         network-connection/main.cpp
         eating-snake/main.cc
         insert-sort/main.cc
-        csp-decode/main.cc)
+        csp-decode/main.cc
+        palin/main.cc)
diff --git a/csp-decode/data.in b/csp-decode/data.in
new file mode 100644
index 0000000..9330744
--- /dev/null
+++ b/csp-decode/data.in
@@ -0,0 +1,11 @@
+10
+770 77 5
+633 1 211
+545 1 499
+683 3 227
+858 3 257
+723 37 13
+572 26 11
+867 17 17
+829 3 263
+528 4 109
diff --git a/palin/data.in b/palin/data.in
new file mode 100644
index 0000000..c832e97
--- /dev/null
+++ b/palin/data.in
@@ -0,0 +1,5 @@
+2
+5
+4 1 2 4 5 3 1 2 3 5
+3
+3 2 1 2 1 3
diff --git a/palin/main.cc b/palin/main.cc
new file mode 100644
index 0000000..9f17e53
--- /dev/null
+++ b/palin/main.cc
@@ -0,0 +1,79 @@
+#include <iostream>
+#include <deque>
+#include <cstring>
+#include <algorithm>
+
+using namespace std;
+
+const int N = 1000005;
+
+int arr[N], brr[N], crr[N], n;
+
+bool calc(char op) {
+    deque<int> a, b;
+    string out, append;
+    out.push_back(op);
+    append.push_back('L');
+    if (op == 'L') {
+        for (int i = 2; i < crr[1]; i++) a.push_back(i);
+        for (int i = n; i > crr[1]; i--) b.push_back(i);
+    } else {
+        for (int i = 1; i < crr[n]; i++) a.push_back(i);
+        for (int i = n - 1; i > crr[n]; i--) b.push_back(i);
+    }
+    while (!a.empty() || !b.empty()) {
+        int x1 = !a.empty() ? a.front() : 0;
+        int x2 = !b.empty() ? b.front() : 0;
+        int y1 = !a.empty() ? a.back() : 0;
+        int y2 = !b.empty() ? b.back() : 0;
+        if (crr[x1] == y1) {
+            out.push_back('L');
+            append.push_back('L');
+            a.pop_front();
+            a.pop_back();
+        } else if (crr[x1] == y2) {
+            out.push_back('L');
+            append.push_back('R');
+            a.pop_front();
+            b.pop_back();
+        } else if (crr[x2] == y1) {
+            out.push_back('R');
+            append.push_back('L');
+            b.pop_front();
+            a.pop_back();
+        } else if (crr[x2] == y2) {
+            out.push_back('R');
+            append.push_back('R');
+            b.pop_front();
+            b.pop_back();
+        } else {
+            return false;
+        }
+    }
+    reverse(append.begin(), append.end());
+    out += append;
+    cout << out << endl;
+    return true;
+}
+
+int main() {
+    int T;
+    cin >> T;
+
+    while (T--) {
+        cin >> n;
+        memset(brr, 0, sizeof brr);
+        n *= 2;
+        crr[0] = -1;
+        for (int i = 1; i <= n; i++) {
+            cin >> arr[i];
+            if (brr[arr[i]]) {
+                crr[brr[arr[i]]] = i;
+                crr[i] = brr[arr[i]];
+            } else {
+                brr[arr[i]] = i;
+            }
+        }
+        if (!calc('L') && !calc('R')) cout << -1 << endl;
+    }
+}