// Arup Guha
// 1/13/2026
// Solution to Kattis Program: Stocks Mania
// https://open.kattis.com/problems/stocksmania

import java.util.*;

public class stocksmania {

	public static void main(String[] args) {

        // Read in the values.
		Scanner stdin = new Scanner(System.in);
		int n = stdin.nextInt();
		int[] vals = new int[n];
		for (int i=0; i<n; i++)
			vals[i] = stdin.nextInt();

		// Just add all positive differences.
		int res = 0;
		for (int i=0; i<n-1; i++)

            // So selectively buy, as shown here.
			if (vals[i] < vals[i+1])
				res += (vals[i+1]-vals[i]);

		System.out.println(res);
	}
}