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;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var sc = new Scanner();
            int n = sc.NextInt();
            int[] h = new int[n];
            for (int i = 0; i < n; i++) h[i] = sc.NextInt();
            
            int ans = 0;
            while (true)
            {
                int head = 0;
                while (head < n && h[head] == 0) head++;
                if (head == n) break;
                int min = h[head];
                int count = 1;
                for (int i = head + 1; i < n; i++)
                {
                    if (h[i] == 0) break;
                    if (h[i] < min) min = h[i];
                    count++;
                }
                ans += min;
                for (int i = 0; i < count; i++) h[head + i] -= min;
            }
            Console.WriteLine(ans);
        }
    }

    class Scanner
    {
        int index = -1;
        string[] buf;

        public Scanner()
        {
        }

        public int NextInt()
        {
            CheckNext();
            return int.Parse(buf[index++]);
        }

        public long NextLong()
        {
            CheckNext();
            return long.Parse(buf[index++]);
        }

        public string NextString()
        {
            CheckNext();
            return buf[index++];
        }

        private void CheckNext()
        {
            if (index >= 0 && index < buf.Length) return;

            buf = Console.ReadLine().Split(' ');
            index = 0;
        }
    }
}