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: Accepted)

from collections import deque

N = int(input())
hhh = list(map(int, input().split()))

# Initial settings
stack = deque()
stack.append(hhh)
n_operation = 0


def operation():
    global stack, n_operation

    flower_heights = stack.pop()
    args_zero_height = [i for i, v in enumerate(flower_heights) if v == 0]
    
    if args_zero_height == []:  # If there is no zero elem.
        flower_heights_minus1 = list(map(lambda x: x-1, flower_heights))
        n_operation += 1
        stack.append(flower_heights_minus1)
    else:  # If there are zero elems
        last_arg_zero = -1
        for i, arg in enumerate(args_zero_height):
            if i == 0:
                # Rightside
                non_zero_heights = flower_heights[:arg]
            else:
                # Middle
                non_zero_heights = flower_heights[last_arg_zero+1:arg]

            if non_zero_heights != []:
                non_zero_heights_minus1 = \
                    list(map(lambda x: x-1, non_zero_heights))
                n_operation += 1
                stack.append(non_zero_heights_minus1)
            last_arg_zero = arg
        # Add leftside
        if last_arg_zero < len(flower_heights)-1:
            non_zero_heights = flower_heights[last_arg_zero+1:]
            # The fucking code (DRY)
            non_zero_heights_minus1 = \
                list(map(lambda x: x-1, non_zero_heights))
            n_operation += 1
            stack.append(non_zero_heights_minus1)


# Do operations while stack is not empty
while stack:
    operation()

print(n_operation)