diff --git a/CMakeLists.txt b/CMakeLists.txt
index e8bedea..288643f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,18 +1,13 @@
-# CMakeList.txt : CMake project for xtfs, include source and define
-# project specific logic here.
-#
-cmake_minimum_required (VERSION 3.16)
-
-
-project ("primetest")
-
-# Add source to this project's executable.s
-
-add_executable (primetest "src/primetest.cpp")
-
-set_property(TARGET primetest PROPERTY CXX_STANDARD 17)
-set_property(TARGET primetest PROPERTY CXX_STANDARD_REQUIRED ON)
-set_property(TARGET primetest PROPERTY CXX_EXTENSIONS OFF)
-
-
-# TODO: Add tests and install targets if needed.
+# CMakeList.txt : CMake project for xtfs, include source and define
+# project specific logic here.
+#
+cmake_minimum_required (VERSION 3.16)
+
+
+project (primetest VERSION 1.0 LANGUAGES CXX)
+
+set_property(TARGET PROPERTY CXX_STANDARD 21)
+set_property(TARGET PROPERTY CXX_STANDARD_REQUIRED ON)
+set_property(TARGET PROPERTY CXX_EXTENSIONS OFF)
+
+add_subdirectory(src)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..89ff6dd
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,8 @@
+# CMakeList.txt
+
+add_executable(primetest primetest.cpp)
+
+add_subdirectory(prime)
+
+
+target_link_libraries( primetest PRIVATE prime )
\ No newline at end of file
diff --git a/src/prime/CMakeLists.txt b/src/prime/CMakeLists.txt
new file mode 100644
index 0000000..a1d8966
--- /dev/null
+++ b/src/prime/CMakeLists.txt
@@ -0,0 +1,16 @@
+# CMakeList.txt
+
+add_library(prime "")
+
+target_sources(prime
+  PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}/prime.cpp
+  PUBLIC
+    ${CMAKE_CURRENT_LIST_DIR}/prime.hpp
+)
+
+target_include_directories(prime
+
+  PUBLIC
+    ${CMAKE_CURRENT_LIST_DIR}
+)
\ No newline at end of file
diff --git a/src/prime/prime.cpp b/src/prime/prime.cpp
new file mode 100644
index 0000000..d2b2aae
--- /dev/null
+++ b/src/prime/prime.cpp
@@ -0,0 +1,17 @@
+#include "prime.hpp"
+
+int Prime::count(int n){
+    int cntout = 0;
+    for( int icnt = 2; ( icnt <= n ); icnt++ ){
+        int ts = 0;
+        for ( int it=icnt; it > 1; --it ){
+            if( (icnt % it) == 0 ) {
+                ts = ts + 1;
+            }
+        }
+        if( ts==1 ){
+            cntout = cntout + 1;
+        }
+    }
+    return cntout;
+}
diff --git a/src/prime/prime.hpp b/src/prime/prime.hpp
new file mode 100644
index 0000000..e6771a6
--- /dev/null
+++ b/src/prime/prime.hpp
@@ -0,0 +1,9 @@
+#ifndef PRIME_HPP
+#define PRIME_HPP
+
+class Prime {
+    public:
+    static int count(int n);
+};
+
+#endif
\ No newline at end of file
diff --git a/src/primetest.cpp b/src/primetest.cpp
index 15c7bc5..dbe50ff 100644
--- a/src/primetest.cpp
+++ b/src/primetest.cpp
@@ -1,27 +1,10 @@
 #include<iostream>
+#include<prime.hpp>
 
 using std::cout;
-
-class Solution {
-    public:
-    static int countPrime(int n){
-        int cntout = 0;
-        for( int icnt = 2; ( icnt <= n ); icnt++ ){
-            int ts = 0;
-            for ( int it=icnt; it > 1; --it ){
-                if( (icnt % it) == 0 ) {
-                    ts = ts + 1;
-                }
-            }
-            if( ts==1 ){
-                cntout = cntout + 1;
-            }
-        }
-        return cntout;
-    }
-};
+using std::endl;
 
 int main(int argc, char** argv){
-        std::cout << Solution::countPrime(50000) << std::endl;
+        std::cout << Prime::count(50000) << std::endl;
     
 }
\ No newline at end of file