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.Generic;

using E = System.Linq.Enumerable;

public class Program
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine());
        var hs = Console.ReadLine().Split().Select(x => int.Parse(x)).ToArray();

        hs = hs.Concat(new [] { 0 }).ToArray();

        var k = 0;
        var max = hs.Max();
        while (max > 0)
        {
            max = 0;
            int l = 0;
            var min = int.MaxValue;
            for (int i = 0; i < hs.Length; i++)
            {
                if (hs[i] > 0)
                {
                    min = Math.Min(min, hs[i]);
                    continue;
                }

                if (l == i)
                {
                    l++;
                    continue;
                }
                
                k += min;
                for (int j = l; j <= i; j++)
                {
                    hs[j] -= min;
                    max = Math.Max(max, hs[j]);
                }
                l = i + 1;
                min = int.MaxValue;
            }
        }

        Console.WriteLine(k);
    }
}