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 JAVA (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.InputStreamReader;


public class Main {

	public static void main(String[] args) throws Exception {
		// TODO ?????????????????????????????????????????????
		BufferedReader breader = getReader();
		int[] ary = getAryMl(breader);
		int maxdf = ary[1] - ary[0] ;
		for( int i = 0 ; i < ary.length ; i++ ) {
			int maxj = i+1;
			if ( maxj == ary.length ) break;
			int mini = i;
			for( int j = i+2 ; j < ary.length ; j++ ) {
				if ( ary[maxj] <= ary[j]) {
					maxj = j;
				}
			}
			for( int k = i+1 ; k < maxj ; k++ ) {
				if ( ary[k] < ary[mini]) {
					mini = k;
				}
			}
			int maxdfw = ary[maxj]- ary[mini];
			if ( maxdf < maxdfw) {
				maxdf = maxdfw ;
			}
			i = maxj;
		}
		System.out.println(maxdf);
		
	}
	public static BufferedReader getReader() {
		return( new BufferedReader(new InputStreamReader(System.in)));
	}
	public static int getInt(BufferedReader br)throws Exception {
		String line = br.readLine();
		return Integer.valueOf(line);
	}
	public static int[] getAry(BufferedReader br)throws Exception {
		String line = br.readLine();
		String[] nstr = line.split(" ");
		int[] n = new int[nstr.length];
		for( int i=0 ; i < nstr.length ; i++ ) {
			n[i] = Integer.valueOf(nstr[i]);
		}
		return n;
	}
	public static int[] getAryMl(BufferedReader br)throws Exception {
		int n = getInt(br);
		int[] ary = new int[n];
		for( int i=0 ; i < n ; i++ ) {
			ary[i] = getInt(br);
		}
		return ary;
	}
	public static void putAry(int[] ary, int num) {
		for( int i = 0; i < num ; i++ ) {
			System.out.print(ary[i]);
			if ( i < num-1) {
				System.out.print(" ");
			}
		}
		System.out.println("");
	}
	public static void putAry(int[] ary) {
		putAry(ary, ary.length ) ;
	}
	public static boolean isPrime(int n) {
		int r = (int)Math.sqrt((double)n)+1;
		for( int j = 2 ; j < r ; j += 1) {
			if ( n%j == 0 ) {
				return false;
			}
		}
		return true;
	}

}