Need help with this runtime of algorithm with double loops that results in 0


I know with absolute certainty that this is the wrong runtime, but I just wanted to show you how I got to it.

for (i = 0; i <= n; i++) do
j = 2*i
while j <= n do
j = j + 1
print(“Hello World”)
end

Then I get the runtime
$Θ(sum_{i=1}^n 1 + n -2i)=Θ(n+n^2-n(n+1))=Θ(0)$??