import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        }

        long sum = 0;
        for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        }
        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[] a = new int[n];
        for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        }

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

        long sum = 0;
        for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        }
        System.out.println(sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        }

        long sum = 0;
        for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        }
        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[] a = new int[n]; a new int[n] n for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            a[i] = sc.nextInt();
        } {
            a[i] = sc.nextInt();
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc long sum = 0; sum 0 for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        } int i=0; int i=0; i 0 i<a.length i a.length a a.length i++ i++ i {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        } {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        } if(i == a.length-1) break; i == a.length-1 i a.length-1 a.length a a.length 1 break; if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            } a[i] > a[i+1] a[i] a i a[i+1] a i+1 i 1 {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            } sum += a[i] - a[i+1] sum a[i] - a[i+1] a[i] a i a[i+1] a i+1 i 1 a[i+1] = a[i+1] + (a[i] - a[i+1]) a[i+1] a i+1 i 1 a[i+1] + (a[i] - a[i+1]) a[i+1] a i+1 i 1 (a[i] - a[i+1]) a[i] a i a[i+1] a i+1 i 1 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[] a = new int[n];
        for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        }

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

        long sum = 0;
        for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        }
        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[] a = new int[n];
        for(int i=0; i<n; i++) {
            a[i] = sc.nextInt();
        }

        long sum = 0;
        for(int i=0; i<a.length; i++) {
            if(i == a.length-1) break;
            if(a[i] > a[i+1]) {
                sum += a[i] - a[i+1];
                a[i+1] = a[i+1] + (a[i] - a[i+1]);
            }
        }
        System.out.println(sum);
    }
}
