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 Rust (1.15.1) (judge verdict: Accepted)


#[allow(dead_code)]
fn rd() -> String {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    input.trim().to_owned()
}

/// 1行の文字を空白で分割してVec<T>にする。
#[allow(dead_code)]
fn rd_vec<T : std::str::FromStr>() -> Vec<T> {
    rd().split_whitespace().map(|x| x.parse().ok().unwrap()).collect()
}

/// 1つの要素を入力で受け取る
#[allow(dead_code)]
fn rd_one<T : std::str::FromStr>() -> T {
    rd().parse().ok().unwrap()
}

/// 複数回read_splitを行う
#[allow(dead_code)]
fn rd_vec_mul<T : std::str::FromStr>(count : i32) -> Vec<Vec<T>> {
    (0..count).map(|_| rd_vec()).collect()
}

/// Vecを1列で出力する
#[allow(dead_code)]
fn op_vec<T : std::fmt::Display>(item : Vec<T>, splitter : char) {
    let cnt = item.len();
    let mut c = 0;
    for i in item.iter() {
        c+=1;
        if cnt > c {print!("{}{}", i, splitter);} else {println!("{}", i);}
    }
}

fn main() {
    let n : usize = rd_one();
    let h : Vec<i32> = rd_vec();
    let mut answer = 0;
    for i in 1.. {
        let mut counter = 0;
        let mut before_under = false;
        if h[0] < i {
            before_under = true;
        } else {
            counter+=1;
        }
        for ni in 1..n {
            if h[ni] < i{
                if before_under {
                    continue;
                }
                before_under = true;
                continue;
            }
            if before_under {
                counter+=1;
                before_under = false;
            }
        }

        if counter == 0 {
            break;
        }
        answer += counter;
    }
    
    println!("{}", answer);
}