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::collections::*;
use std::io::*;
use std::cmp;
#[allow(dead_code)]
struct Io<'a> {
    r: BufReader<StdinLock<'a>>,
    w: BufWriter<StdoutLock<'a>>,
    buf: VecDeque<String>,
    buf_str: String,
}
#[allow(dead_code)]
impl<'a> Io<'a> {
    fn r<T: std::str::FromStr>(&mut self) -> T {
        if self.buf.len() == 0 {
            self.r.read_line(&mut self.buf_str).unwrap();
            for w in self.buf_str.split_whitespace() {
                self.buf.push_back(w.to_owned());
            }
            self.buf_str.clear();
        }
        self.buf
            .pop_front()
            .unwrap()
            .parse()
            .unwrap_or_else(|_| panic!())
    }
    fn w<T: std::fmt::Display>(&mut self, v: T) {
        writeln!(self.w, "{}", v).unwrap();
    }
    fn iter<'b, T: std::str::FromStr>(&'b mut self) -> IoIter<'a, 'b, T> {
        IoIter {
            io: self,
            p: std::marker::PhantomData,
        }
    }
}
#[allow(dead_code)]
struct IoIter<'a: 'b, 'b, T: std::str::FromStr> {
    io: &'b mut Io<'a>,
    p: std::marker::PhantomData<T>,
}
#[allow(dead_code)]
impl<'a, 'b, T: std::str::FromStr> Iterator for IoIter<'a, 'b, T> {
    type Item = T;
    fn next(&mut self) -> Option<T> {
        Some(self.io.r())
    }
}
fn main() {
    let stdin = stdin();
    let stdout = stdout();
    let r = BufReader::new(stdin.lock());
    let w = BufWriter::new(stdout.lock());
    let io = Io {
        r,
        w,
        buf: VecDeque::new(),
        buf_str: String::new(),
    };
    unsafe {
        problem(io);
    }
}


unsafe fn problem(mut io: Io) {
    let n: usize = io.r();

    let mut min: isize = io.r();
    let mut max_prof = std::isize::MIN;
    for r in io.iter::<isize>().take(n - 1) {
        max_prof = cmp::max(max_prof, r - min);
        min = cmp::min(min, r);
    }

    io.w(max_prof);
}