Matlab If Else Statement

The prompt of the question I have to do is: " The value of y is defined in terms of x by y=ln(0.5-x), write a function myfun(x) that takes some value x and does the following:

If x is greater or equal to 0.5 the function should caluculate y by using the negative value of that x and assign the result to z

If the value of x smaller than 0.5 the function should return the value z where z is calculated as the following

z=y^n

where n is (x+(100*x)) rounded to the nearest integer.

In my code, under a new scipt I created the function saved as "myfunx" as follows;

function myfun(x)
if x>=0.5
    y=ln(0.5-(-x))
    z=y^n 
else
    y=ln(0.5-x)
    z=y^n 
end

and in the command window when I test it with such value as x=1 and call the funciton myfunx, and it reads error and claims

"Not enough input arguments.

Error in myfunx (line2)

if x>=0.5

However I do not know what Im doing wrong or how I could fix this, any tips or ideas that could help me solve this would be appreciated thank you!