diff --git a/hf16/3.cpp b/hf16/3.cpp
new file mode 100644
index 0000000..ee2a315
--- /dev/null
+++ b/hf16/3.cpp
@@ -0,0 +1,27 @@
+#include <bits/stdc++.h>
+#include <iostream>
+using namespace std;
+
+
+// harmadik feladat
+vector<int> common(vector<int> a, vector<int> b) {
+    vector<int> out;
+    for (int i = 0; i < a.size(); i++) {
+        for (int j = 0; j < b.size(); j++) {
+            if (a[i] == b[j]) {
+                out.push_back(a[i]);
+            }
+        }
+    }
+    return out;
+}
+
+int main() {
+    vector<int> a = {1,2,3,4,5,6};
+    vector<int> b = {2,4,6,8,10};
+    vector<int> out = common(a,b);
+
+    for (int i = 0; i < out.size(); i++) {
+        cout<<out[i]<<" ";
+    }
+}
\ No newline at end of file