Leftmost Non-Zero Subtract

You are given an array of non-negative integers. Repeatedly find the leftmost nonzero element; with its value x, process the elements from that position to the right one by one, subtracting x from an element only if its current value is at least x; in each round, add x to the total. Once the array is all zeros, output the total.

Standard input/output and this site's supplementary ranges follow this problem's description.

输入格式

The first line contains n, and the second line contains n integers. The source gives the value range 0≤a[i]≤10000; since direct simulation is O(n²), this site narrows n to 1≤n≤1000 so that it finishes within the time limit.

输出格式

Output the total accumulated during the process, as one integer.

样例 1

输入：

5
0 2 2 0 3

输出：

3

样例 2

输入：

3
4 4 0

输出：

4

样例 3

输入：

3
1 2 3

输出：

3