import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    }
}
 import java.util.*; util.* java public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    }
} Main public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    } main {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int cur = 0; cur 0 long sum = 0; sum 0 for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	} {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	} int x = sc.nextInt(); x sc.nextInt() sc.nextInt sc if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    } cur <= x cur x {
    	        cur = x;
    	    } cur = x cur x {
    	        sum += cur - x;
    	    } sum += cur - x sum cur - x cur x System.out.println(sum) System.out.println System.out System System.out sum String[] args args public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    }
} public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    }
} Main
import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int cur = 0;
    	long sum = 0;
    	for (int i = 0; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (cur <= x) {
    	        cur = x;
    	    } else {
    	        sum += cur - x;
    	    }
    	}
    	System.out.println(sum);
    }
}

