import java.io.PrintWriter;
import java.util.*;

public class Main {
    static Scanner scanner;
    static PrintWriter out;
    public static void main(String[] args) {
        scanner = new Scanner(System.in);
        out = new PrintWriter(System.out);

        long n = nextInt();
        nextLine();
        long ans = 0;
        long max = 0;
        long te;
        for (int i = 0; i < n; i++) {
            te = nextLong();
            if (te > max) {
                max = te;
            } else {
                ans += max - te;
            }
        }
        out.println(ans);
        out.flush();
    }

    public static int getNC(char c) {
        switch (c) {
            case '0':
                return 0;
            case '1':
                return 1;
            case '2':
                return 2;
            case '3':
                return 3;
            case '4':
                return 4;
            case '5':
                return 5;
            case '6':
                return 6;
            case '7':
                return 7;
            case '8':
                return 8;
            case '9':
                return 9;
        }
        return 0;
    }

    public static void println(Object o) {
        out.println(o);
    }

    public static void print(Object o) {
        out.print(o);
    }

    public static void printf(String format, Object... o) {
        out.printf(format, o);
    }

    public static String next() {
        return scanner.next();
    }

    public static int nextInt() {
        return Integer.parseInt(scanner.next());
    }

    public static long nextLong() {
        return Long.parseLong(scanner.next());
    }

    public static double nextDouble() {
        return Double.parseDouble(scanner.next());
    }

    public static short nextShort() {
        return Short.parseShort(scanner.next());
    }

    public static float nextFloat() {
        return Float.parseFloat(scanner.next());
    }

    public static void printYes() {
        System.out.println("Yes");
    }

    public static void printYES() {
        System.out.println("YES");
    }

    public static void printNo() {
        System.out.println("No");
    }

    public static void printNO() {
        System.out.println("NO");
    }

    public static String nextLine() {
        return scanner.nextLine();
    }

    public static double distance(double x, double y, double x2, double y2) {
        return Math.sqrt((x2 - x) * (x2 - x) + (y2 - y) * (y2 - y));
    }

    public static int MOD = 1_000_000_007;
    public static int MAX = 100000;
    public static long[] fac = new long[MAX];
    public static long[] finv = new long[MAX];
    public static long[] inv = new long[MAX];

    public static void combinit() {
        fac[0] = fac[1] = 1;
        finv[0] = finv[1] = 1;
        inv[1] = 1;
        for (int i = 2; i < MAX; i++) {
            fac[i] = fac[i - 1] * i % MOD;
            inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
            finv[i] = finv[i - 1] * inv[i] % MOD;
        }
    }

    public static long combination(int n, int k) {
        if (n < k || n < 0 || k < 0) return 0;
        return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
    }

    public static long factorial(long n) {
        return n <= 0 ? 1 : n * factorial(n - 1);
    }
}

Measured memory_bytes: 52668