import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz