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)

n = int(input())
ls = list(map(int,input().split()))
def sub(p,q):
    return p-q
i = 0
p = 1
new=[0 for _ in range(n)]
s = [1 for _ in range(n)]
while ls[ls.index(max(ls))]>0:
    for j in range(len(ls)):
        if j == n-1:
            if ls[j] > 0:
                new[j] = p
            else:
                pass
        else:
            if (ls[j] <= 0) and (ls[j+1] <= 0):
                pass
            elif (ls[j] <= 0) and (ls[j+1] > 0):
                p += 1
            elif (ls[j] > 0) and (ls[j+1] > 0):
                new[j] = p
            else:
                new[j] = p
    if (sum(new) == n) and (len(list(set(new))) == 1):
        i += 1
    else:
        i += len(list(set(new))) -1
    ls = list(map(sub,ls,s))
    new = [0]*n
    p = 1
print(i)