diff --git a/src/main/java/ic/doc/ReversePolishStack.java b/src/main/java/ic/doc/ReversePolishStack.java
index fc0d0a0..ff6f0f9 100644
--- a/src/main/java/ic/doc/ReversePolishStack.java
+++ b/src/main/java/ic/doc/ReversePolishStack.java
@@ -1,7 +1,15 @@
 package ic.doc;
 
+import java.util.Stack;
+
 public class ReversePolishStack {
+  private final Stack<IntOperator> stack = new Stack<>();
+
   public int getSize() {
-    return 0;
+    return stack.size();
+  }
+
+  public void push(IntOperator intOperator) {
+    stack.push(intOperator);
   }
 }
diff --git a/src/test/java/ic/doc/ReversePolishStackTest.java b/src/test/java/ic/doc/ReversePolishStackTest.java
index 5fff47e..ba2bca0 100644
--- a/src/test/java/ic/doc/ReversePolishStackTest.java
+++ b/src/test/java/ic/doc/ReversePolishStackTest.java
@@ -12,4 +12,12 @@ public class ReversePolishStackTest {
   public void reversePolishStackEmptyInitially() {
     assertThat(reversePolishStack.getSize(), is(0));
   }
+
+  @Test
+  public void canPushToReversePolishStack() {
+    reversePolishStack.push(new IntOperator(0, args -> 1));
+    assertThat(reversePolishStack.getSize(), is(1));
+    reversePolishStack.push(new IntOperator(0, args -> 2));
+    assertThat(reversePolishStack.getSize(), is(2));
+  }
 }