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;

namespace Algorithm
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var array = Console.ReadLine().Split().Select(z => int.Parse(z)).ToArray();

            var commit = new bool[n];
            var arrayMultiple = new int[n];
            for (var i = 0; i < n; i++)
            {
                commit[i] = false;
                arrayMultiple[i] = array[i] * 2;
                if (array[i] == 0) commit[i] = true;
            }

            var total = 0;

            // commitが全部trueになるまでループする
            while (commit.Any(v => v == false))
            {
                var start = int.MaxValue;
                var end = n;

                for (var i = 0; i < n; i++)
                {
                    if (array[i] + 1 <= arrayMultiple[i])
                    {
                        start = i;
                        break;
                    }
                }

                for (var i = start+1; i < n; i++)
                {
                    if (commit[i])
                    {
                        end = i;
                        break;
                    }
                }

                var min = int.MaxValue;
                for (var i = start; i < end; i++)
                {
                    min = Math.Min(arrayMultiple[i] - array[i], min);
                }

                for (var i = start; i < end; i++)
                {
                    array[i] += min;
                }
                total += min;

                for (var i = start; i < end; i++)
                {
                    if (array[i] == arrayMultiple[i])
                    {
                        commit[i] = true;
                    }
                }

            }
            Console.WriteLine(total);
        }
    }
}