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;

public static class Program
{
    public static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var vals = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
        var result = Enumerable.Range(0, n).Select(x => 0).ToArray();
        var cnt = 0;
        for (int i = 1; i <= vals.Max(); i++)
        {
            var aryIdx = vals.Select((val, idx) => new { Idx = idx, Val = val })
                .Where(x => x.Val >= i).Select(x => x.Idx).ToArray();
            if (aryIdx.Length == 0)
                continue;
            var start = aryIdx.Min();
            for (int j = 0; j < aryIdx.Length; j++)
            {
                if (j == aryIdx.Length - 1)
                {
                    for (int k = start; k <= j; k++)
                        result[k]++;
                    cnt++;
                }
                else if (aryIdx[j + 1] - aryIdx[j] > 1)
                {
                    for (int k = start; k <= j; k++)
                        result[k]++;
                    start = aryIdx[j + 1];
                    cnt++;
                }
            }
        }
        Console.WriteLine(cnt);
    }
}