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;

class Program {
  static void Main(string[] args) {
    Console.ReadLine();
    List<int> h = Console.ReadLine().Split(' ').Select(e => int.Parse(e)).ToList();

    var q = new Queue<Tuple<int, int>>();
    q.Enqueue(Tuple.Create(0, h.Count));
  
    int ans = 0;

    while (q.Count > 0) {
      var e = q.Dequeue();
      if (e.Item1 == e.Item2) {
        continue;
      }

      int m = 101;
      for (int i = e.Item1; i < e.Item2; i++) {
        if (h[i] < m) {
          m = h[i];
        } 
      }
      
      ans += m;

      int next = -1;
      for (int i = e.Item1; i < e.Item2; i++) {
        if (h[i] > m) {
          h[i] -= m;
          if (next == -1) {
            next = i;
          }
        } else if (next != -1) {
          q.Enqueue(Tuple.Create(next, i));
          next = -1;
        }
      }

      if (next != -1) {
        q.Enqueue(Tuple.Create(next, e.Item2));
      }
    }

    Console.WriteLine(ans);
  }
}