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 Go (1.6) (judge verdict: Accepted)

package main

import "fmt"

func main() {
	var n int
	fmt.Scan(&n)

	h := make([]int, n)
	for i:=range h {
		fmt.Scan(&h[i])
	}
	g := make([]int, n-1)
	if n == 1 {
		fmt.Println(h[0])
		return
	}

	for i:=1;i<n;i++ {
		if h[i-1] <= h[i] {
			g[i-1] = 1
		} else {
			g[i-1] = -1
		}
	}
	var ans int
	if g[0] == -1 {
		ans = h[0]
	} else {
		ans = 0
	}
	for i:=1;i<n-1;i++ {
		if g[i-1] == -1 && g[i] == 1 {
			ans -=  h[i]
		} else if g[i-1] == 1 && g[i] == -1 {
			ans += h[i]
		}
	}
	if g[n-2] == 1 {
		ans += h[n-1]
	}

	fmt.Println(ans)
}