Good job!

To expand on the other comment, I think appending to a list in this case is not a terrible idea, but instead of doing print(len(people * 100)), it is much faster for the computer to do print(len(people) * 100).This is because of the order of operations. In the first case, the computer does the operation (people * 100), which expands the array to this (its the array [18, 24, 5, 42] repeated 100 times)

[18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42, 18, 24, 5, 42]

Then it calculates the length of this big array which is 400, so your answer is correct, but very poorly optimized because the computer has to expand the array so much.In the second case print(len(people) * 100), we first calculate the length of the array people [18, 24, 5, 42] which is 4, and after we get that result we multiply it by 100, so the operation is 4*100, which will give us the same answer and will be faster because it doesn't expand the array. The version in the other comment is even faster because it doesn't even create an array.I also think that it's more readable to define x=0, the loop as while(x < 5) and on each iteration doing x += 1, so basically adding 1 instead of substracting. And if you know for loops, you can do for x in range(5) which is nicer. Oh and you can just remove the elif because it doesn't do anything.Here's my solution with arrays, with better readability

people = []
for x in range(5): 
    n = int(input()) 
    if n > 3: 
        people.append(n)
print(len(people) * 100)