import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        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();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        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 long[] a = new long[n]; a new long[n] n for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        } int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
            a[i] = sc.nextLong();
        } {
            a[i] = sc.nextLong();
        } a[i] = sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc long max = a[0]; max a[0] a 0 long ans = 0l; ans 0l for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        } int i = 1; int i = 1; i 1 i < a.length i a.length a a.length i++ i++ i {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        } {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        } if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            } a[i] <= max a[i] a i max {
                ans += max - a[i];
            } ans += max - a[i] ans max - a[i] max a[i] a i {
                max = a[i];
            } max = a[i] max a[i] a i 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();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextLong();
        }
        long max = a[0];
        long ans = 0l;
        for (int i = 1; i < a.length; i++) {
            if(a[i] <= max) {
                ans += max - a[i];
            } else {
                max = a[i];
            }
        }
        System.out.println(ans);
    }
}