import java.math.BigDecimal;
import java.util.Scanner;
class Main {
    public static void main(final String[] args) {
        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();
        int max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    }
}
/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