The program below uses six temporary variables a, b, c, d, e, f. a = 1 b = 10…

The program below uses six temporary variables a, b, c, d, e, f.

a = 1
b = 10
c = 20
d = a + b
e = c + d
f = c + e
b = c + e
e = b + f
d = 5 + e

return d + f

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