diff --git a/ShippingCosts/Implementations/ShippingCostCalculatorBase.cs b/ShippingCosts/Implementations/ShippingCostCalculatorBase.cs
index 3017e99..8cc2b3e 100644
--- a/ShippingCosts/Implementations/ShippingCostCalculatorBase.cs
+++ b/ShippingCosts/Implementations/ShippingCostCalculatorBase.cs
@@ -20,7 +20,16 @@ public abstract class ShippingCostCalculatorBase(ICountryDistanceProvider countr
     /// <returns>Sum of the longest and shortest side</returns>
     protected static int SumOfLongestAndShortestSides(IMeasuredBox box)
     {
-        // TODO
-        return -1;
+        int[] sides = [box.Width, box.Height, box.Depth];
+        for (int i = 0; i < sides.Length; i++)
+        {
+            if (sides[i] <= 0)
+            {
+                return 0;
+            }
+        }
+        
+        Array.Sort(sides);
+        return sides[0] + sides[2];
     }
 }