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 Python (3.4.3) (judge verdict: Wrong Answer)

import sys
sys.setrecursionlimit(10**8)
N = int(input())

H = list(map(lambda x: int(x) + 1, input().split()))

def it(items, count):
    if not items:
        return 0
    if len(items) == 1:
        return items[0] + count

    ids = [-1]
    for i in range(len(items)):
        items[i] -= 1
        if items[i] <= 0:
            ids.append(i)
    ids.append(len(items))

    ans = 0
    for i in range(len(ids)-1):
        next_items = items[ids[i]+1:ids[i+1]]
        ans += it(next_items, count+1)
        if next_items:
            count = -1

    return ans

print(it(H, -1))