import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
        int maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	}
} 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 maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
        int maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
        int maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int maxA = sc.nextInt(); maxA sc.nextInt() sc.nextInt sc long res = 0; res 0 for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        } int i=1; int i=1; i 1 i<N i N i++ i++ i {
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        } {
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        } int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc maxA = Math.max(maxA,A) maxA Math.max(maxA,A) Math.max Math maxA A res = res + maxA - A res res + maxA - A res + maxA res maxA A System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
        int maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
        int maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	}
} 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 maxA = sc.nextInt();
        long res = 0;
        for(int i=1; i<N; i++){
            int A = sc.nextInt();
            maxA = Math.max(maxA,A);
            res = res + maxA - A;
            
        }
		System.out.println(res);
	}
}