Python, how I can find sum of this elements?

Question

Find the sum of n elements of the following row of numbers:
1, -0.5, 0.25, -0.125 ...
The number of elements (n) is entered from the keyboard.

Answer 1

You're looking for something like this?

l = []
for i in range(int(input())):
    if i%2 ==0:
        l.append(1/2**i)
    else:
        l.append(-(1/2**i))
print(sum(l))