An imaginary computer has four data registers (R0 to R3),102

An imaginary computer has four data registers (R0 to R3),1024 words in memory,and 16 different instruction (add,subtract,etc.).What is the minimum size of an instruction in bits if a typical instruction uses the following format:add 565 R2.
如果有好的解答,我自然会加分,先谢过了