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