import java.util.Scanner;
public class Main
{
    public static void main(String[] args)
    {
        long sl=0;
        Scanner sc=new Scanner(System.in);
        int n= sc.nextInt();
        int a[]=new int[n];
        for(int i=0;i<n;i++)
        {
            a[i]=sc.nextInt();
        }
        for(int j=0;j<n-1;j++)
        {
            if(a[j]>=a[j+1])
            {
                sl=sl+(a[j]-a[j+1]);
                a[j+1]=a[j+1]+(a[j]-a[j+1]);
            }
            
        }
        
        System.out.println(sl);
    }
}
/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