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 AtCoder
{
    class Program
    {
        public static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int[] h = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            Console.WriteLine("{0}", f(h, 0, N - 1));
        }

        public static int f(int[] nums, int l, int r)
        {
            for (int i = l; i < r + 1; i++)
            {
                if (nums[i] > 0) { nums[i]--; continue; }
                // Console.WriteLine("{0} {1} {2}", i, l, r);
                return (l == r) ? 0 :
                       (i == l) ? f(nums, i + 1, r) :
                       (i == r) ? 1 + f(nums, l, i - 1)
                                : 1 + f(nums, l, i - 1) + f(nums, i + 1, r);
            }
            return 1 + f(nums, l, r);
        }
    }
}