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)

import copy
N = int(input())
series = list(map(int,input().split()))
final = [0 for _ in range(len(series))]
count = 0
while series != final:
	start = 0
	end = 0
	for i in range(len(series)):
		if series[i] == 0:
			if start != i:
				end = i
				m = min(series[start:end])
				for j in range(start,end):
					series[j] -= m
				count += m
			else:
				start = i + 1
		elif i == len(series)-1:
			end = i
			m = min(series[start:i+1])
			for j in range(start,i+1):
				series[j] -= m
			count += m
print(count)