diff --git a/task3/main-ab.cpp b/task3/main-ab.cpp
new file mode 100644
index 0000000..4fc8575
--- /dev/null
+++ b/task3/main-ab.cpp
@@ -0,0 +1,83 @@
+#include <iostream>
+#include <QSemaphore>
+#include <QThread>
+#include <QCoreApplication>
+
+/*
+ * Barlas Chpt 3 Ex 12:
+    Create three threads, each printing out the letters A, B, and C.
+    The printing must adhere to these rules:
+        • The total number of Bs and Cs that have been output at any
+          point in the output string cannot exceed the total number
+          of As that have been output at that point.
+        • After a C has been output, another C cannot be output until
+          one or more Bs have been output.
+    Use semaphores to solve the problem.
+*/
+
+class Printer {
+private:
+    QSemaphore &lockBC_;
+    QSemaphore &lockC_;
+
+    QString name_;
+
+public:
+    explicit Printer(QSemaphore &lockBC, QSemaphore &lockC, QString name) : lockBC_(lockBC), lockC_(lockC),
+                                                                            name_(name) {};
+
+    void printA() {
+        this->lockBC_.release(1);
+        std::cout << name_.toStdString() << " A\n";
+    }
+
+    void printB() {
+        if (this->lockBC_.tryAcquire(1, 10000)) {
+            if (this->lockC_.available() == 0) {
+                this->lockC_.release(1);
+            }
+            std::cout << name_.toStdString() << " B\n";
+        }
+    }
+
+    void printC() {
+        if (this->lockBC_.tryAcquire(1, 10000)) {
+            if (this->lockC_.tryAcquire(1, 10000)) {
+                std::cout << name_.toStdString() << " C\n";
+            } else {
+                this->lockBC_.release(1);
+            }
+        }
+    }
+};
+
+class Worker : public QThread {
+private:
+    Printer printer_;
+
+public:
+    Worker(QSemaphore &lockBC, QSemaphore &lockC, QString tname) : printer_(lockBC, lockC, tname) {};
+
+protected:
+    void run() {
+        printer_.printA();
+        printer_.printB();
+        printer_.printC();
+    }
+};
+
+
+int main(int argc, char *argv[]) {
+    QCoreApplication app(argc, argv);
+    QSemaphore lockC(1);
+    QSemaphore lockBC(0);
+
+    int N = 3;
+    Worker *workers[N];
+    for (int i = 0; i < N; i++) {
+        workers[i] = new Worker(lockBC, lockC, QString("Thread %1").arg(i));
+        workers[i]->start();
+    }
+
+    return app.exec();
+}