Add multilingual language and systems learning tracks

en/swift-practice-20261101/lesson-3/main.swift

@@ -0,0 +1,9 @@
+func remaining(_ total: Int, _ done: Int) -> Int {
+    return max(0, total - done)
+}
+
+precondition(remaining(4,1) == 3)
+precondition(remaining(4,4) == 0)
+precondition(remaining(4,5) == 0)
+precondition(remaining(0,0) == 0)
+print("Passed")