Long story short - to create a light transport Antonov bureau took a prototype which was built to evaluate the Coandă effect - hence how engines are located, they was supposed to create ariflow at the upper part of the wing, decreasing takeoff and landing distances and generating additional lift force.

Although, the effect was bit of a headache - for example, single-engine failure was really a mess, because it was creating a huge difference in lift force. Engines were eventually moved into a safer positinon, but after that additional Coandă effect lift force was just about 5-7%.

Although, high-ranked army officers loved the design at the first sight - they said engines are positioned very safe for unpaved airfields, so the protoptye was adopted for MP and eventually became An-72/74.