diff --git a/calculator.cpp b/calculator.cpp
index 23b2bb3..3c63184 100644
--- a/calculator.cpp
+++ b/calculator.cpp
@@ -4,3 +4,8 @@ int Calculator::Add (int a, int b)
 {
     return a + b;
 }
+
+int Calculator::Sub (int a, int b)
+{
+    return Add (a, -b);
+}
diff --git a/calculator.h b/calculator.h
index 5813ec9..84ff414 100644
--- a/calculator.h
+++ b/calculator.h
@@ -5,6 +5,7 @@ class Calculator
 {
     public:
         int Add (int, int);
+        int Sub (int, int);
 };
 
 #endif//CALCULATOR_H