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: Wrong Answer)

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

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
        int n = readInt(r);
        
        if (n <= 1) {
            output(-1);
            return;
        } else {
            int maxDelta = -1;
            int r_i = readInt(r);
            for (int i = 0;i < (n -1);i++) {
                int r_j = readInt(r);
                
                int delta = r_j - r_i;
                if (delta > 0 && delta > maxDelta) {
                    maxDelta = delta;
                }

                if (r_i > r_j) {
                    r_i = r_j;
                }
            }
            
            output(maxDelta);
        }
    }

    public static void output(int x) {
        System.out.println(x);
    }

    public static int readInt(BufferedReader r) throws Exception {
        return Integer.parseInt(r.readLine());
    }
}