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;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp
{
    class Program
    {
        static int ans = 0;

        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var str = Console.ReadLine();
            var strs = str.Split(' ');

            var hs = new List<int>();
            foreach (var item in strs)
            {
                hs.Add(int.Parse(item));
            }

            Watering(hs);

            Console.WriteLine(ans);
        }

        static void Watering(List<int> hs)
        {

            for (int i = 0; i < hs.Count; i++)
            {
                if (hs[i] != 0)
                {
                    break;
                }

                if (i == hs.Count - 1)
                {
                    return;
                }
            }

            if (hs.Count == 1)
            {
                ans += hs[0];
                return;
            }

            while (!hs.Contains(0))
            {
                for (int i = 0; i < hs.Count; i++)
                {
                    hs[i]--;
                }
                ans++;
            }

            var borderIndex = hs.IndexOf(0);

            if (borderIndex != 0)
            {
                Watering(hs.Take(borderIndex).ToList());
            }

            if (borderIndex != hs.Count - 1)
            {
                Watering(hs.Skip(borderIndex + 1).Take(hs.Count - borderIndex).ToList());
            }
        }
    }
}