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