
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.math.BigInteger; BigInteger java.math import java.util.*; util.* java import java.util.stream.Collectors; Collectors java.util.stream import java.util.stream.Stream; Stream java.util.stream public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    } main {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    } FastReader fr  = new FastReader(); fr new FastReader() int n = fr.nextInt(); n fr.nextInt() fr.nextInt fr long[] arr = new long[n]; arr new long[n] n for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            arr[i] = fr.nextInt();
        } {
            arr[i] = fr.nextInt();
        } arr[i] = fr.nextInt() arr[i] arr i fr.nextInt() fr.nextInt fr long ans = 0; ans 0 long maxTillNow = arr[0]; maxTillNow arr[0] arr 0 for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        } {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        } if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            } arr[i]<maxTillNow arr[i] arr i maxTillNow {
                ans+=(maxTillNow-arr[i]);
            } ans+=(maxTillNow-arr[i]) ans (maxTillNow-arr[i]) maxTillNow arr[i] arr i if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            } arr[i]>maxTillNow arr[i] arr i maxTillNow {
                maxTillNow = arr[i];
            } maxTillNow = arr[i] maxTillNow arr[i] arr i System.out.println(ans) System.out.println System.out System System.out ans String[] args args static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    } FastReader BufferedReader br; br StringTokenizer st; st public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        } FastReader {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        } br = new BufferedReader(new
                    InputStreamReader(System.in)) br new BufferedReader(new
                    InputStreamReader(System.in)) String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } next {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } IOException e {
                    e.printStackTrace();
                } e.printStackTrace() e.printStackTrace e {
                    st = new StringTokenizer(br.readLine());
                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } nextLine {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } String str = ""; str "" try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                str = br.readLine();
            } str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    }
} public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    }
} Main

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) throws Exception {
        FastReader fr  = new FastReader();
        int n = fr.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = fr.nextInt();
        }
        long ans = 0;
        long maxTillNow = arr[0];
        for (int i = 1; i < n; i++) {
            if(arr[i]<maxTillNow){
                ans+=(maxTillNow-arr[i]);
            }
            else if(arr[i]>maxTillNow){
                maxTillNow = arr[i];
            }
        }
        System.out.println(ans);
    }
}
