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())
h = list(map(int,input().split()))

ans = 0
s = 0
e = 0
while max(h) != 0:  
    for k in range(N):
        if h[k] != 0:
            s = k
            break
    if s == N-1:
        ans += h[N-1]
        break
    for k in range(s+1,N):
        e = k
        if h[k] == 0:
            break
        if k == N-1:
            e += 1
    t = min(h[s:e])
    for k in range(s,e):
        h[k] -= t
    ans += t
print(ans)