Number by 3
The sequence of real numbers
an is given. Find the sum and the number of positive elements which indexes are divisible by 3.
The number of elements n (n ≤ 100) in a sequence is given in the first line. Next line contains n real numbers, each value does not exceed 100 by absolute value.
Print in one line the number of required elements and their sum with 2 digits after the decimal point.
6 6 7.5 2.1 2.0 0 -3