import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    }

} import java.util.Scanner; Scanner java.util public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int[] a = new int[N]; a new int[N] N for(int i = 0; i < N; i++)
            a[i] = sc.nextInt(); int i = 0; int i = 0; i 0 i < N i N i++ i++ i a[i] = sc.nextInt(); a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc long answer = 0; answer 0 for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        } int i = 1; int i = 1; i 1 i < N i N i++ i++ i {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        } {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        } if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            } a[i] >= a[i - 1] a[i] a i a[i - 1] a i - 1 i 1 continue; {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            } answer += a[i - 1] - a[i] answer a[i - 1] - a[i] a[i - 1] a i - 1 i 1 a[i] a i a[i] = a[i - 1] a[i] a i a[i - 1] a i - 1 i 1 System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    }

} public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    }

} Main
import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] a = new int[N];
        for(int i = 0; i < N; i++)
            a[i] = sc.nextInt();

        long answer = 0;
        for(int i = 1; i < N; i++) {
            if(a[i] >= a[i - 1])
                continue;
            else {
                answer += a[i - 1] - a[i];
                a[i] = a[i - 1];
            }
        }

        System.out.println(answer);
    }

}
