import java.util.*;

class Main {
	public static void main(String[] args) {
		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();
		}
		sc.close();
		long ans = 0;
		for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		}
		System.out.println(ans);
	}
}
 import java.util.*; util.* java class Main {
	public static void main(String[] args) {
		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();
		}
		sc.close();
		long ans = 0;
		for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		}
		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		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();
		}
		sc.close();
		long ans = 0;
		for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		}
		System.out.println(ans);
	} main {
		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();
		}
		sc.close();
		long ans = 0;
		for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		}
		System.out.println(ans);
	} 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 sc.close() sc.close sc long ans = 0; ans 0 for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		} 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] - A[i];
				//System.out.println(A[i]);
			}
		} {
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		} if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			} 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] - A[i];
				//System.out.println(A[i]);
			} 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 A[i-1] - A[i] A[i-1] A i-1 i 1 A[i] A i System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;

class Main {
	public static void main(String[] args) {
		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();
		}
		sc.close();
		long ans = 0;
		for(int i=1;i<N;++i){
			if(A[i]<A[i-1]){
				ans += A[i-1] - A[i];
				A[i] += A[i-1] - A[i];
				//System.out.println(A[i]);
			}
		}
		System.out.println(ans);
	}
}

