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

namespace C
{
    public class Program
    {
        static void Main(string[] args)
        {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            Solve();
            Console.Out.Flush();
        }

        public static void Solve()
        {
            var n = int.Parse(Console.ReadLine());
            var hi = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray();
            var current = new int[hi.Length];

            Console.WriteLine(Dfs(current, hi, 0, hi.Length - 1));
        }

        static int Dfs(int[] current, int[] target, int left, int right)
        {
            if (left == right) return target[left];
            if (left > right) return 0;

            var min = 101;
            for (var i = left; i <= right; i++)
            {
                min = Math.Min(min, target[i]);
            }
            if (min == 101) return 0;

            var mid = -1;
            for (var i = left; i <= right; i++)
            {
                current[i] += min;
                target[i] -= min;
                if (target[i] == 0) mid = i;
            }

            var leftValue = Dfs(current, target, left, mid - 1);
            var rightValue = Dfs(current, target, mid + 1, right);
            return min + leftValue + rightValue;
        }
    }
}