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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;
public class Main{
    public static void main(String[] args) throws IOException{
        BufferedReader bf = 
            new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(bf.readLine());
        String[] str = bf.readLine().split(" ");
        List<Integer> h = new ArrayList<>();
        for(int i = 0; i < N; i++){
            h.add(Integer.parseInt(str[i]));
        }
        System.out.println(count(h));
    }
    public static Integer min(List<Integer> data){
        Integer min = data.get(0);
        for(int i = 1; i < data.size(); i++){
            Integer value = data.get(i);
            if(value < min){
                min = value;
            }
        }
        return min;
    }
    public static int count(List<Integer> data){
        int min = min(data);
        for(int i = 0; i < data.size(); i++){
            Integer value = data.get(i);
            data.set(i, value-min);
        }
        boolean zero = true;
        List<List> a = new ArrayList<>();
        for(int i = 0; i < data.size(); i++){
            int value = data.get(i);
            if(zero && value > 0){
                a.add(new ArrayList<Integer>());
                a.get(a.size()-1).add(value);
                zero = false;
            } else if(!zero){
                if(value > 0){
                    a.get(a.size()-1).add(value);
                } else{
                    zero = true;
                }
            }
        }
        int answer = min;
        for(int i = 0; i < a.size(); i++){
            answer += count(a.get(i));
        }
        return answer;
    }
}