Python The function f3 gets a list of int numbers and any int number x. it returns as a result how many pairs of elements exist such that their sum is x. Must not take the same element 2 times as 1 pair. If no such pairs exist, then result is 0. example : a= [2,3,2,3,2] f3 (a, 5) == 6 we get the following pairs whose sum is 5 : a[0], a [1] a[1], a [2] a[2], a [3] a [3], a[4] a [0], a [3] a[1], a [4] Complete the missing code of f2, as follows: def f3(a,x): return Requirements : The code to be completed MUST be written ONLY in the signed place, after the word return. The function must NOT be recursive