import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	}
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	} main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int max = sc.nextInt(); max sc.nextInt() sc.nextInt sc long ans = 0; ans 0 for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        } {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        } int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            } a <= max a max {
                ans += max - a;
            } ans += max - a ans max - a max a {
                max = a;
            } max = a max a System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int max = sc.nextInt();
        long ans = 0;
        for (int i = 1; i < n; i++) {
            int a = sc.nextInt();
            if (a <= max) {
                ans += max - a;
            } else {
                max = a;
            }
        }
        System.out.println(ans);
	}
}