B'You are given a set of n segments on a line [L_i; R_i] . All 2n segment endpoints are pairwise distinct integers. The set is laminar -- any two segments are either disjoint or one of them contains the other. Choose a non-empty subsegment [l_i, r_i] with integer endpoints in each segment ( L_i <= l_i < r_i <= R_i ) in such a way that no two subsegments intersect (they are allowed to have common endpoints though) and the sum of their lengths ( sum_{i=1}^n r_i - l_i ) is maximized. The first line contains a single integer n ( 1 <= n <= 2 cdot 10^3 ) -- the number of segments. The i -th of the next n lines contains two integers L_i and R_i ( 0 <= L_i < R_i <= 10^9 ) -- the endpoints of the i -th segment. All the given 2n segment endpoints are distinct. The set of segments is laminar. On the first line, output the maximum possible sum of subsegment lengths. On the i -th of the next n lines, output two integers l_i and r_i ( L_i <= l_i < r_i <= R_i ), denoting the chosen subsegment of the i -th segment. The example input and the example output are illustrated below. '...