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: Accepted)

def f(ls):
    if len(ls) == 0:
        return 0
    cnt = 0
    if not 0 in ls:
        min_ = min(ls)
        ls = [l - min_ for l in ls]
        cnt += min_
    divs = []
    s = 0
    for i, l in enumerate(ls):
        if l == 0:
            if i == 0:
                s = 1
            else:
                divs.append(ls[s:i])
                s = i + 1
    if l != 0:
        if s == i:
            divs.append([ls[s]])
        else:
            divs.append(ls[s:i+1])
    cnt_ = sum([f(d) for d in divs])
    return cnt + cnt_

n = int(input())
ls_ = [int(i) for i in input().split()]
print(f(ls_))