import java.util.*;
public class Main{
	
	
	private static Scanner sc=new Scanner(System.in);
	
	public static void main(String []args){
		long n=sc.nextInt();
		long curMax=0,temp,totalHeight=0;
		for(int i=0;i<n;i++){
			temp=sc.nextInt();
			if(curMax<temp)
				curMax=temp;
			totalHeight+=(curMax-temp);
		}
		System.out.println(totalHeight);
	}
}
/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