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;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = ReadInt();
            var h = ReadArrayInt();
            var ans = 0;
            if (h.Min() != 0)
            {
                ans = h.Min();
                h = h.Select(i => i - ans).ToArray();
            }
            while (true)
            {
                var start = -1;
                var end = -1;
                var min = int.MaxValue;
                for (int i = 0; i < N; i++)
                {
                    if (h[i] != 0)
                    {
                        start = i;
                        end = i;
                        min = h[i];
                        break;
                    }
                }
                if (start == -1) break;
                for (int i = start + 1; i < N; i++)
                {
                    if (h[i] == 0) break;
                    else
                    {
                        end = i;
                        if (h[i] < min) min = h[i];
                    }
                }
                ans += min;
                for (int i = start; i <= end; i++)
                {
                    h[i] -= min;
                }
            }

            Console.WriteLine(ans);
            Console.ReadLine();
        }

        static string Read() { return Console.ReadLine(); }
        static int ReadInt() { return int.Parse(Read()); }
        static long ReadLong() { return long.Parse(Read()); }
        static int[] ReadArrayInt() { return Read().Split(' ').Select(s => int.Parse(s)).ToArray(); }
        static long[] ReadArrayLong() { return Read().Split(' ').Select(s => long.Parse(s)).ToArray(); }
    }
}