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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		long count = 0;
		for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		}

		System.out.println(count);
	}

} 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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		long count = 0;
		for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		}

		System.out.println(count);
	}

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

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

		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc long[] a = new long[n]; a new long[n] n for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			a[i] = sc.nextLong();
		} {
			a[i] = sc.nextLong();
		} a[i] = sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc long count = 0; count 0 for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		} int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		} {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		} long s = a[i-1] - a[i]; s a[i-1] - a[i] a[i-1] a i-1 i 1 a[i] a i if(s > 0) {
				a[i] += s;
				count += s;
			} s > 0 s 0 {
				a[i] += s;
				count += s;
			} a[i] += s a[i] a i s count += s count s System.out.println(count) System.out.println System.out System System.out count 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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		long count = 0;
		for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		}

		System.out.println(count);
	}

} 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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		long count = 0;
		for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		}

		System.out.println(count);
	}

} 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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		long count = 0;
		for(int i = 1; i < n; i++) {
			long s = a[i-1] - a[i];
			if(s > 0) {
				a[i] += s;
				count += s;
			}
		}

		System.out.println(count);
	}

}
