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;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder_Tutorial
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            List<int> hList = Console.ReadLine().Split().Select(_ => int.Parse(_)).ToList();

            int count = 0;
            while (hList.Any(num => 0 < num))
            {
                if (hList.All(num => 0 < num))
                {
                    int min = hList.Min();
                    for (int i = 0; i < hList.Count; i++)
                        hList[i] -= min;
                    count += min;
                }
                else
                {
                    int start = 0;
                    for (int i = 1; i < hList.Count; i++)
                    {
                        if (hList[i-1] == 0 && 0 < hList[i])
                        {
                            start = i;
                            break;
                        }
                    }
                    
                    for (int i = start; i < hList.Count && hList[i] != 0; i++)
                    {
                        hList[i]--;
                    }
                    count++;
                }
            }
            Console.WriteLine(count);
        }
    }
}