import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	}
}
 import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] tall = new int[n]; tall new int[n] n for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
          tall[i]= sc.nextInt();
        } {
          tall[i]= sc.nextInt();
        } tall[i]= sc.nextInt() tall[i] tall i sc.nextInt() sc.nextInt sc long ans =0; ans 0 for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      } int l = 0; int l = 0; l 0 l<n-1 l n-1 n 1 l++ l++ l {
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      } {
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      } if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	} tall[l] > tall[l+1] tall[l] tall l tall[l+1] tall l+1 l 1 {
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	} ans += tall[l] - tall[l+1] ans tall[l] - tall[l+1] tall[l] tall l tall[l+1] tall l+1 l 1 tall[l+1] = tall[l] tall[l+1] tall l+1 l 1 tall[l] tall l System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		// 身長の入力
      	int[] tall = new int[n];
		for(int i=0;i<n;i++){
          tall[i]= sc.nextInt();
        }
    
    /*--------------------------------*/
      long ans =0;
      for(int l = 0; l<n-1;l++){
    	if(tall[l] > tall[l+1]){
      		ans += tall[l] - tall[l+1];
      		tall[l+1] = tall[l];
     	}
      }
      System.out.println(ans);
	}
}

