B'You are given a regular N -sided polygon. Label one arbitrary side as side 1 , then label the next sides in clockwise order as side 2 , 3 , ... , N . There are A_i special points on side i . These points are positioned such that side i is divided into A_i + 1 segments with equal length. For instance, suppose that you have a regular 4 -sided polygon, i.e., a square. The following illustration shows how the special points are located within each side when A = [3, 1, 4, 6] . The uppermost side is labelled as side 1 . You want to create as many non-degenerate triangles as possible while satisfying the following requirements. Each triangle consists of 3 distinct special points (not necessarily from different sides) as its corners. Each special point can only become the corner of at most 1 triangle. All triangles must not intersect with each other. Determine the maximum number of non-degenerate triangles that you can create. A triangle is non-degenerate if it has a positive area. The first line consists of an integer N ( 3 <= q N <= q 200 ,000 ). The following line consists of N integers A_i ( 1 <= q A_i <= q 2 cdot 10^9 ). Output a single integer representing the maximum number of non-degenerate triangles that you can create. Explanation for the sample input/output #1 One possible construction which achieves maximum number of non-degenerate triangles can be seen in the following illustration. Explanation for the sample input/output #2 One possible construction which achieves maximum number of non-degenerate triangles can be seen in the following illustration. '...