B"We say an infinite sequence a_{0}, a_{1}, a_2, ldots is non-increasing if and only if for all i ge 0 , a_i ge a_{i+1} . There is an infinite right and down grid. The upper-left cell has coordinates (0,0) . Rows are numbered 0 to infinity from top to bottom, columns are numbered from 0 to infinity from left to right. There is also a non-increasing infinite sequence a_{0}, a_{1}, a_2, ldots . You are given a_0 , a_1 , ldots , a_n ; for all i>n , a_i=0 . For every pair of x , y , the cell with coordinates (x,y) (which is located at the intersection of x -th row and y -th column) is white if y<a_x and black otherwise. Initially there is one doll named Jina on (0,0) . You can do the following operation. Note that multiple dolls can be present at a cell at the same time; in one operation, you remove only one. Your goal is to make all white cells contain 0 dolls. What's the minimum number of operations needed to achieve the goal? Print the answer modulo 10^9+7 . The first line of input contains one integer n ( 1 <= n <= 2 cdot 10^5 ). The second line of input contains n+1 integers a_0,a_1, ldots,a_n ( 0 <= a_i <= 2 cdot 10^5 ). It is guaranteed that the sequence a is non-increasing. Print one integer -- the answer to the problem, modulo 10^9+7 . Consider the first example. In the given grid, cells (0,0),(0,1),(1,0),(1,1) are white, and all other cells are black. Let us use triples to describe the grid: triple (x,y,z) means that there are z dolls placed on cell (x,y) . Initially the state of the grid is (0,0,1) . One of the optimal sequence of operations is as follows: Now all white cells contain 0 dolls, so we have achieved the goal with 5 operations. "...