diff --git a/src/g2_2025_interfaces/CMakeLists.txt b/src/g2_2025_interfaces/CMakeLists.txt
index 9bb5c01..a97f387 100644
--- a/src/g2_2025_interfaces/CMakeLists.txt
+++ b/src/g2_2025_interfaces/CMakeLists.txt
@@ -8,12 +8,14 @@ endif()
 # find dependencies
 find_package(ament_cmake REQUIRED)
 find_package(rosidl_default_generators REQUIRED)
+find_package(builtin_interfaces REQUIRED)
 
 rosidl_generate_interfaces(${PROJECT_NAME}
     "msg/Student.msg"
     "msg/Exam.msg"
-    "srv/Exam.srv"
+    "srv/Exams.srv"
     "action/Retake.action"
+    DEPENDENCIES builtin_interfaces
 )
 
 ament_export_dependencies(rosidl_default_runtime)
diff --git a/src/g2_2025_interfaces/msg/Exam.msg b/src/g2_2025_interfaces/msg/Exam.msg
index 67ad017..8d1beb9 100644
--- a/src/g2_2025_interfaces/msg/Exam.msg
+++ b/src/g2_2025_interfaces/msg/Exam.msg
@@ -1,2 +1,3 @@
 string lecture_name
 int32 result
+builtin_interfaces/Time timestamp
diff --git a/src/g2_2025_interfaces/msg/Student.msg b/src/g2_2025_interfaces/msg/Student.msg
index 566c1cc..fa576b2 100644
--- a/src/g2_2025_interfaces/msg/Student.msg
+++ b/src/g2_2025_interfaces/msg/Student.msg
@@ -1,2 +1,3 @@
 string student_name
 string lecture_name
+builtin_interfaces/Time timestamp
diff --git a/src/g2_2025_interfaces/package.xml b/src/g2_2025_interfaces/package.xml
index e596ef9..42e2940 100644
--- a/src/g2_2025_interfaces/package.xml
+++ b/src/g2_2025_interfaces/package.xml
@@ -10,7 +10,9 @@
   <buildtool_depend>ament_cmake</buildtool_depend>
 
   <build_depend>rosidl_default_generators</build_depend>
+  <build_depend>builtin_interfaces</build_depend>
   <exec_depend>rosidl_default_runtime</exec_depend>
+  <exec_depend>builtin_interfaces</exec_depend>
   <member_of_group>rosidl_interface_packages</member_of_group>
 
   <test_depend>ament_lint_auto</test_depend>
diff --git a/src/g2_2025_interfaces/srv/Exam.srv b/src/g2_2025_interfaces/srv/Exam.srv
deleted file mode 100644
index 8e9945c..0000000
--- a/src/g2_2025_interfaces/srv/Exam.srv
+++ /dev/null
@@ -1,5 +0,0 @@
-# Request
-string student_name
-string lecture_name
----
-float32 result
diff --git a/src/g2_2025_interfaces/srv/Exams.srv b/src/g2_2025_interfaces/srv/Exams.srv
new file mode 100644
index 0000000..d5f62f3
--- /dev/null
+++ b/src/g2_2025_interfaces/srv/Exams.srv
@@ -0,0 +1,7 @@
+# Request
+string student_name
+string lecture_name
+int32[] exam_grades
+---
+# Response
+int32 result  # Final result