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 Ruby (2.3.3) (judge verdict: Accepted)

N = gets.to_i
H = gets.chomp.split(" ").map(&:to_i)

def block_subtraction(f, t)
  mi = H[f..t].min
  (f..t).each{|i| H[i] -= mi}
  ret = mi
  w_f = -1
  (f..t).each{|i|
    w_f = i if w_f == -1 && H[i] > 0
    (ret += block_subtraction(w_f, i-1); w_f = -1) if w_f > -1 && H[i] == 0
  }
  ret += block_subtraction(w_f, t) if w_f > -1
  ret
end

puts block_subtraction(0, N-1)