//package  com.company;


import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    } main {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        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 prev=-1; prev -1 1 long ans=0; ans 0 for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        } int i=0; int i=0; i 0 i<N i N ++i ++i i {
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        } {
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        } int a=sc.nextInt(); a sc.nextInt() sc.nextInt sc if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            } prev>a prev a {
                ans+=prev-a;
            } ans+=prev-a ans prev-a prev a {
                prev=a;
            } prev=a prev a 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);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    }
} public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    }
} Main
//package  com.company;


import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int prev=-1;
        long ans=0;//1000000*1000000*1000000;
        for(int i=0;i<N;++i){
            int a=sc.nextInt();
            if(prev>a){
                ans+=prev-a;
            }else{
                prev=a;
            }
        }
        System.out.println(ans);
    }
}