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 dfs(L):
    if len(L) == 0:
        return 0

    ret = min(L)
    L = [e - ret for e in L]
    L2 = []
    for i, e in enumerate(L):
        if e == 0:
            ret += dfs(L2)
            L2 = []
        else:
            L2.append(e)

    ret += dfs(L2)
    return ret

def main():
    n = int(input())
    H = [int(e) for e in input().split()]

    print(dfs(H))

if __name__ == "__main__":
    main()