import java.util.Scanner;

public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	}
}
 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[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = new int[n]; a new int[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 int pmax = a[0]; pmax a[0] a 0 long s = 0; s 0 for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		} int i= 1; int i= 1; i 1 i<n i n i++ i++ i {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		} {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		} int d = pmax - a[i]; d pmax - a[i] pmax a[i] a i if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			} d >= 0 d 0 {
				s += d;
			} s += d s d {
				pmax = a[i];
			} pmax = a[i] pmax a[i] a i System.out.println(s) System.out.println System.out System System.out s String[] args args public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	}
} public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	}
} 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[] a = new int[n];
		for( int i= 0; i<n ; i++ ) {
			a[i] = sc.nextInt();
		}
		
		int pmax = a[0];
		long s = 0;
		for( int i= 1; i<n ; i++ ) {
			int d = pmax - a[i];
			if( d >= 0 ) {
				s += d;
			}else {
				pmax = a[i];
			}
			
		}
		
		System.out.println(s);
	}
}

