N = 4000
d = 0.05 
alpha = 0.08

z = qnorm(1-alpha/2)
z

n1 =(4*(N-1)*d^2/(N*z^2)+1/N)^{-1}
n = ceiling(n1)
n

# ako u drugom vrticu dobio p=1/3
p = 1/3
n1 = ((N-1)*d^2/(N*z^2*p*(1-p))+1/N)^{-1}
n = ceiling(n1)
n