import java.util.*;
import java.lang.*;
import java.io.*;

public class Main {
	public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	}
} import java.util.*; util.* java import java.lang.*; lang.* java import java.io.*; io.* java public class Main {
	public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	}
} Main public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	} main {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	} Scanner in=new Scanner(System.in); in new Scanner(System.in) int t t k k i=0 i 0 j=0 j 0 sum=0; sum 0 double m; m long l=0; l 0 int n=in.nextInt(); n in.nextInt() in.nextInt in int a[]=new int[n]; a new int[n] n for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            } i=0; i=0 i 0 i<n i n i++ i++ i {
                a[i]=in.nextInt();
                
            } {
                a[i]=in.nextInt();
                
            } a[i]=in.nextInt() a[i] a i in.nextInt() in.nextInt in i=0 i 0 while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            } i<n-1 i n-1 n 1 {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            } if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               } a[i]>a[i+1] a[i] a i a[i+1] a i+1 i 1 {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               } l+=a[i]-a[i+1] l 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 i 1 a[i] a i i++ i System.out.println(l) System.out.println System.out System System.out l String[] args args public class Main {
	public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	}
} public class Main {
	public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	}
} Main
import java.util.*;
import java.lang.*;
import java.io.*;

public class Main {
	public static void main (String[] args) {
		//code
	Scanner in=new Scanner(System.in);
        int t,k,i=0,j=0,sum=0;
        double m;
        long l=0;
            int n=in.nextInt();
            int a[]=new int[n];
            for(i=0;i<n;i++)
            {
                a[i]=in.nextInt();
                
            }
          i=0;
            while(i<n-1)
            {
               if(a[i]>a[i+1])
               {
                   l+=a[i]-a[i+1];
                  // System.out.println("l="+l);
                   a[i+1]=a[i];
                  // System.out.println("a[i+1]="+a[i+1]);
               }i++;
            }
            System.out.println(l);

               
	}
}