input: def evaluate_model_accuracy(X_train, y_train, X_test, y_test):
      """Evaluate the accuracy of a machine-learning model.
      
      >>> evaluate_model_accuracy(X_train, y_train, X_test, y_test)
      Accuracy: 0.95
      """
output:     from sklearn.linear_model import LogisticRegression
      model = LogisticRegression()
      model.fit(X_train, y_train)
      accuracy = model.score(X_test, y_test)
      print(f"Accuracy: {accuracy:.2f}")