Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

class Program
{
    static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var d = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
        var ans = rec(d, 0, d.Length);
        Console.WriteLine(ans);
    }

    static int rec(int[] d, int x, int y)
    {
        if (x == y) return 0;

        var min = int.MaxValue;
        for (int i = x; i < y; i++)
        {
            min = Math.Min(min, d[i]);
        }

        for (int i = x; i < y; i++)
        {
            d[i] -= min;
        }

        var ans = min;
        for (int l = x, r = x; r <= y; r++)
        {
            if (r != y && d[r] != 0) continue;
            if (l < r) ans += rec(d, l, r);
            l = r + 1;
        }

        return ans;
    }
}