import java.lang.*;
import java.util.*;

class Stock {
	public static int maxProfit(int[] prices) {
		int s = 0;
		int e = prices.length - 1;
		int low = Integer.MAX_VALUE;
		int high = 0;
		while (s < e) {
			if (prices[s] < low)
				low = prices[s];
			if (prices[e] > high)
				high = prices[e];
			s++;
			e--;
		}
		return high - low > 0 ? high - low : 0;
	}

	public static void main(String[] args) {
		int[] prices = {7, 1, 5, 3, 6, 4};
		System.out.println(maxProfit(prices));
	}
}