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 numpy as np
n = int(input())
h0 = [int(i) for i in input().split()]
h = np.zeros(n,dtype = int)
x = np.zeros(n,dtype = int)
#最小値
def minh(h,x):
  tmp1 = 100
  for i in range(n):
    if x[i] == 0:
      if h0[i] <= tmp1:
        tmp1 = h0[i]
  return tmp1
#水やり
def mizu(h,x,tmp):
  for i in range(n):
    if x[i] == 0:
      h[i] = tmp
    if h0[i] == tmp:
      x[i] = 1
#分割数
def bunnkatu(x):
  for i in range(n):
    if i == 0:
      if x[i] == 0:
        s = 1
      else:
        s = 0
    else:
      if x[i] == 0 and x[i-1] == 1:
        s += 1
  return s

def main():
  tmp = min(h0)
  ans = tmp
  mizu(h,x,tmp)
  while tmp < max(h0):
    tmp0 = minh(h,x)
    s = bunnkatu(x)
    mizu(h,x,tmp0)
    ans += s*(tmp0 - tmp)
    tmp = tmp0
  return ans

ans = main()
print(ans)