Python пойдёт? Если да, то вот
R2 = float(input())
R3 = float(input())
R4 = float(input())
R = (R2*R3*R4)/((R3*R4)+(R2*R4)+(R2*R3))
print(R)
end = input('input anything to close program')
Python пойдёт? Если да, то вот
R2 = float(input())
R3 = float(input())
R4 = float(input())
R = (R2*R3*R4)/((R3*R4)+(R2*R4)+(R2*R3))
print(R)
end = input('input anything to close program')