import java.util.*;

class Main{
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]){
        int N=sc.nextInt();
        long n=0,p=sc.nextLong(),res=0;
        for(int i=1;i<N;i++){
            n=sc.nextLong();
            if(p>n){
                res+=p-n;
            }
            else{
                p=n;
            }
        }
        System.out.println(res);
    }
}

/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