import java.util.*;
 
class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    //人数
    int n = sc.nextInt();
    //身長
    long[] h = new long[n];
    
    for(int i = 0;i < n;i++){
      h[i] = sc.nextLong();
    }
    
    
    
    long[] step = new long[n];
    for(int i = 0;i < n;i++){
      step[i] = 0;
    }
    long ans = 0;
    for(int i = 1;i < n;i++){
      if(h[i - 1] > h[i]){
        step[i] = h[i - 1] - h[i];
        h[i] += step[i];
      }
    }
    
    for(int i = 0;i < n;i++){
      ans += step[i];
    }
    System.out.print(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