Problem:
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Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency $R_t$ at a certain time $t$ ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where $j > i$ .

Input

The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t = 0, 1, 2, ... n-1$) are given in order.

Output

Print the maximum value in a line.

Constraints

$2 \leq n \leq 200,000$

$1 \leq R_t \leq 10^9$

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

Solution in Rust (judge verdict: Accepted)

fn main() {
    let n = read::<usize>();
    let mut r = Vec::new();

    for _ in 0..n {
        r.push(read::<i32>());
    }

    println!("{}", max_profit(r));
}

/// 後戻りできないタイプの最大の差を求める
/// ex. 為替レート 4->3->1 : -2(4と3の-1が最大)
fn max_profit(r: Vec<i32>) -> i32 {
    let len = r.len();
    // jまでにある最小値
    let mut minv = r[0];
    // 一番大きな差
    let mut maxv = r[1] - r[0];
    for j in 1..len {
        if r[j] - minv > maxv { 
            maxv = r[j] - minv;
        }
        if minv > r[j] {
            minv = r[j];
        }
    }
    maxv
}

/// 標準入力から一行を読み取り、指定の型に変換する関数
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}