import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    } 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 long count=0; count 0 for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        } int i=0; int i=0; i 0 i<N i N i++ i++ i {
            A[i]=sc.nextLong();
        } {
            A[i]=sc.nextLong();
        } A[i]=sc.nextLong() A[i] A i sc.nextLong() sc.nextLong sc for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        } int i=0; int i=0; i 0 i<N-1 i N-1 N 1 i++ i++ i {
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        } {
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        } if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            } A[i]>A[i+1] A[i] A i A[i+1] A i+1 i 1 {
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            } count+=A[i]-A[i+1] count A[i]-A[i+1] A[i] A i A[i+1] A i+1 i 1 A[i+1]+=A[i]-A[i+1] A[i+1] A i+1 i 1 A[i]-A[i+1] A[i] A i A[i+1] A i+1 i 1 System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long A[] =new long[N];
        long count=0;
        
        for(int i=0;i<N;i++){
            A[i]=sc.nextLong();
        }
        
        for(int i=0;i<N-1;i++){
            if(A[i]>A[i+1]){
                count+=A[i]-A[i+1];
                A[i+1]+=A[i]-A[i+1];
            }
        }
        
        System.out.println(count);
    }
}
