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 PyPy3 (2.4.0) (judge verdict: Runtime Error)

#import numpy as np

N = int(input())
h_list = list(map(int, input().split(" ")))
#h_list = np.asarray(h_list)

def calc(group):
    out = 0
    while True:
        #print("group", group)
        min_val = min(group)
        #group -= min_val # 1
        #zero_list = np.where(group == 0)[0] #1
        zero_list = [elm_i for elm_i, elm in enumerate(group) if elm == 0]
        group = [elm - min_val for elm in group]
        out += min_val

        #cond1 = group.shape[0] - 1 in zero_list # 1
        cond1 = len(group) - 1 in zero_list
        cond2 = 0 in zero_list

        #if group.shape[0] == 1:
        if len(group) == 1:
            #assert group[0] == 0
            break
        else:
            if cond1: 
                zero_list = zero_list[:-1]
                group = group[:-1]
            if cond2:
                zero_list = zero_list[1:]
                group = group[1:]

            if not cond1 and not cond2:
                break

            #if group.shape[0] == 0:
            if len(group) == 0:
                break


    #if group.shape[0] <= 1:
    if len(group) <= 1:
        pass
    else:
        start_i = -1
        for end_i in zero_list:
            child_group = group[start_i+1: end_i]
            #print("child_group", child_group)
            out += calc(child_group)
            start_i = end_i

        child_group = group[start_i+1:]
        #if child_group.shape[0] >= 1:
        if len(child_group) >= 1:
            #print("child_group", child_group)
            out += calc(child_group)

    return out

out = calc(h_list)
print(out)