import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
		

	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
		

	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
		

	} Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int n = stdIn.nextInt(); n stdIn.nextInt() stdIn.nextInt stdIn int[] a = new int[n]; a new int[n] n for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			a[i] = stdIn.nextInt();
		} {
			a[i] = stdIn.nextInt();
		} a[i] = stdIn.nextInt() a[i] a i stdIn.nextInt() stdIn.nextInt stdIn long ans = 0; ans 0 for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				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-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		} {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		} if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			} a[i-1] > a[i] a[i-1] a i-1 i 1 a[i] a i {
				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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
		

	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = stdIn.nextInt();
		}
		long ans = 0;
		
		for(int i = 1; i < n; i++) {
			if(a[i-1] > a[i]) {
				ans += a[i-1] - a[i];
				a[i] = a[i-1];
			}
		}
		
		System.out.println(ans);
		

	}

}
