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

namespace C_GrandGarden
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var h_list = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            int[] flowerBed = new int[n];

            int water_count = 0;
            var dis_list = flowerBed.Select((x, i) => h_list[i] - x).ToArray();

            for (int i = 0; i < n;)
            {
                //差が0以外になるまで増やす
                i += dis_list.BeginEnd(i, n).TakeWhile(x => x == 0).Count();
                var count = dis_list.BeginEnd(i, n).TakeWhile(x => x > 0).Count();

                water_count += Watering(flowerBed, h_list, i, i + count);

                i += count;
            }

            Console.WriteLine(water_count);
        }

        public static int Watering(int[] flowerBed, int[] h_list, int begin, int end)
        {
            if (begin >= end)
            {
                return 0;
            }

            for (int i = begin; i < end; i++)
            {
                flowerBed[i]++;
            }

            int water_count = 1;
            var dis_list = flowerBed.Select((x, i) => h_list[i] - x).ToArray();

            for (int i = begin; i < end;)
            {
                //差が0以外になるまで増やす
                i += dis_list.BeginEnd(i, end).TakeWhile(x => x == 0).Count();
                var count = dis_list.BeginEnd(i, end).TakeWhile(x => x > 0).Count();

                water_count += Watering(flowerBed, h_list, i, i + count);

                i += count;
            }

            return water_count;
        }

    }

    public static class Extensions
    {
        public static IEnumerable<T> BeginEnd<T>(this T[] list, int begin, int end)
        {
            for (int i = begin; i < end; i++)
            {
                yield return list[i];
            }
        }
    }
}