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)

use std::io;
use std::str::FromStr;

fn read_line() -> String {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    s
}

macro_rules! from_line {
    ($($a:ident : $t:ty),+) => {
        $(let $a: $t;)+
        {
            let _line = read_line();
            let mut _it = _line.trim().split_whitespace();
            $($a = _it.next().unwrap().parse().unwrap();)+
                assert!(_it.next().is_none());
        }
    };
}

fn main() {

    from_line!(n: u64);
    let mut v = Vec::new();
    for _ in 0..n {
        let stdin = io::stdin();
        let mut buf = String::new();
        stdin.read_line(&mut buf).ok();
        let mut it = buf.split_whitespace().map(|n| usize::from_str(n).unwrap());
        v.push(it.next().unwrap());
    }

    let mut max: i64 = -1000000000;
    let mut min = v[0] as i64;
    for i in 1..n {
        if max < v[i as usize] as i64 - min {
            max = v[i as usize] as i64 - min;
        }
        if min > v[i as usize] as i64 {
            min = v[i as usize] as i64;
        }

    }
    println!("{}", max);

}