import java.util.Scanner;


public class Main {

	public static void main(String[] args)  {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
	}

}

 import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args)  {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(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 = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(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 = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(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 = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] a = new int[n]; a new int[n] n for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		} int i = 0 ; int i = 0 ; i 0 i < n i n i++ i++ i {
			a[i] = Integer.parseInt(sc.next());
		} {
			a[i] = Integer.parseInt(sc.next());
		} a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc Long ans = 0l; ans 0l for(int i = 1 ; i < n ; i++) {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		} int i = 1 ; int i = 1 ; i 1 i < n i n i++ i++ i {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		} {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		} if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			} 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 = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(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 = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
	}

} Main
import java.util.Scanner;


public class Main {

	public static void main(String[] args)  {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		
		for(int i = 0 ; i < n ; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		
		Long ans = 0l;
		for(int i = 1 ; i < n ; i++) {
			
			if(a[i] < a[i-1]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
	}

}


