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)

=begin
－－－－－－－－－－－－－－
N = 数列の長さ
h = 花の高さの最終目標
ans = 操作回数
－－－－－－－－－－－－－－
1: 数列の先頭の値を取り出し 残った数列 - 先頭の値 を 配列が空になるまで繰り返す
  1.1: 先頭の値が 正の数 の場合は ans に加算し、操作を続ける (負の数の場合 ans への加算は行わない: 操作しすぎた数を戻している作業になる)
2: ans を出力する 
=end

N = gets.to_i;
h = gets.split.map(&:to_i);
ans = 0;

while h.empty? == false do
  a = h.shift;
  ans += a if a > 0;
  h.map!{|v| v - a};
end

p ans