In the game Num cannons, using mathematics, you can protect the virtual world from the invasion of colorful balloons. It seems to you that the falling balls are not a problem, but imagine that there are so many of them that you cannot see the white color and then you need to get rid of them. We installed four numbered guns. You need to choose an action: subtraction, multiplication, division or addition. A dropping ball has a mathematical example on its side. You must quickly solve it, and the correct answer is the number of the gun from which you need to shoot. Any other weapon just won't work.