a = 10

b = 20

c = 30

d=a+c

f=c+c

b=c+e

e=b+f

d=5+e

return d+f

Assuming that all the above operations take their operands from registers, the minimum number of registers needed to execute this program without spilling is

 Assuming that all the above operations take their operands from registers, the minimum number of registers needed to execute this program without spilling is