import java.util.*;

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 < n; i++) {
      a[i] = sc.nextLong();
    }
    long sum = 0;
    for (int i = 0; i < n - 1; i++) {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    }
    System.out.println(sum);
  }
} import java.util.*; util.* java 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 < n; i++) {
      a[i] = sc.nextLong();
    }
    long sum = 0;
    for (int i = 0; i < n - 1; i++) {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    }
    System.out.println(sum);
  }
} 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 < n; i++) {
      a[i] = sc.nextLong();
    }
    long sum = 0;
    for (int i = 0; i < n - 1; i++) {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    }
    System.out.println(sum);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    long[] a = new long[n];
    for (int i = 0; i < n; i++) {
      a[i] = sc.nextLong();
    }
    long sum = 0;
    for (int i = 0; i < n - 1; i++) {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    }
    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 long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++) {
      a[i] = sc.nextLong();
    } int i = 0; int i = 0; i 0 i < n i n 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 sum = 0; sum 0 for (int i = 0; i < n - 1; i++) {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    } int i = 0; int i = 0; i 0 i < n - 1 i n - 1 n 1 i++ i++ i {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    } {
      if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      }
    } if(a[i] > a[i + 1]) {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      } a[i] > a[i + 1] a[i] a i a[i + 1] a i + 1 i 1 {
        long dai = a[i] - a[i + 1];
        sum = sum + dai;
        a[i + 1] = a[i];
      } long dai = a[i] - a[i + 1]; dai a[i] - a[i + 1] a[i] a i a[i + 1] a i + 1 i 1 sum = sum + dai sum sum + dai sum dai a[i + 1] = a[i] a[i + 1] a i + 1 i 1 a[i] a i System.out.println(sum) System.out.println System.out System System.out sum String[] args args
import java.util.*;

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