//Coded By Visnunathan

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.lang.*;

public class Main {
    static int[] arr;
    static int n,k;
    public static void main(String[] args) {
        FastScanner sc=new FastScanner();
        // int T=sc.nextInt();
        // for (int tt=0; tt<T; tt++) {
            n = sc.nextInt();
            arr = sc.readArray(n);
            int ans = 0, max = arr[0];
            for(int i=1; i<n; i++) {
                if(max > arr[i]) ans+=max-arr[i];
                max = Math.max(max,arr[i]);
            }
            System.out.println(ans);
        //}
    }

    static final Random random=new Random();
    
    static void ruffleSort(int[] a) {
        int n=a.length;//shuffle, then sort 
        for (int i=0; i<n; i++) {
            int oi=random.nextInt(n), temp=a[oi];
            a[oi]=a[i]; a[i]=temp;
        }
        Arrays.sort(a);
    }
    
    static class FastScanner {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st=new StringTokenizer("");
        String next() {
            while (!st.hasMoreTokens())
                try {
                    st=new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            return st.nextToken();
        }
        
        int nextInt() {
            return Integer.parseInt(next());
        }
        int[] readArray(int n) {
            int[] a=new int[n];
            for (int i=0; i<n; i++) a[i]=nextInt();
            return a;
        }
        long nextLong() {
            return Long.parseLong(next());
        }
    }

    
}
