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: Runtime Error)

def countA(A):
    global cnt
    if len(A)==1:
        cnt += A[0]
    else:
        amin = min(A)
        A = [A[i]-amin for i in range(len(A))]
        cnt += amin
        while A:
            if A[0]==0:
                A.pop(0)
            elif A[-1]==0:
                A.pop()
            else:break
        B = []
        for i in range(1,len(A)):
            if A[i]==0 and A[i-1]==0:
                B.append(i)
        C = []
        for i in range(len(A)):
            if i not in B:
                C.append(A[i])
        C0 = []
        for i in range(len(C)):
            if C[i]==0:
                C0.append(i)
        if len(C0)==0 and len(C)>0:
            countA(C)
        else:
            cur = 0
            for c in C0:
                countA(C[cur:c])
                cur = c+1
            countA(C[cur:])
            
N = int(input())
H = list(map(int,input().split()))
cnt = 0
countA(H)
print(cnt)