import java.util.Scanner;

 
public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	}
}

 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();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	}
} Main public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	} main {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n  = sc.nextInt(); n sc.nextInt() sc.nextInt sc long max = 0; max 0 long ans = 0; ans 0 for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		} {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		} int height = sc.nextInt(); height sc.nextInt() sc.nextInt sc if(max < height) {
				max = height;
			} max < height max height {
				max = height;
			} max = height max height ans += max - height ans max - height max height System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc String[] args args public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	}
} public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	}
} Main
import java.util.Scanner;

 
public class Main {
 
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int n  = sc.nextInt();
		long max = 0;
		long ans = 0;
		
		for(int i = 0; i < n; i++) {
			int height = sc.nextInt();
			if(max < height) {
				max = height;
			}
			ans += max - height;
		}
		
		System.out.println(ans);
		sc.close();
	}
}


