#include <bits/stdc++.h>
using namespace std;
string findSum(string str1, string str2) {
  if (str1.length() > str2.length()) swap(str1, str2);
  string str = "";
  int n1 = str1.length(), n2 = str2.length();
  reverse(str1.begin(), str1.end());
  reverse(str2.begin(), str2.end());
  int carry = 0;
  for (int i = 0; i < n1; i++) {
    int sum = ((str1[i] - '0') + (str2[i] - '0') + carry);
    str.push_back(sum % 10 + '0');
    carry = sum / 10;
  }
  for (int i = n1; i < n2; i++) {
    int sum = ((str2[i] - '0') + carry);
    str.push_back(sum % 10 + '0');
    carry = sum / 10;
  }
  if (carry) str.push_back(carry + '0');
  reverse(str.begin(), str.end());
  return str;
}
int main() {
  int n;
  cin >> n;
  vector<int> vec;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    vec.push_back(x);
  }
  int m = vec[0];
  string sum;
  for (int i = 1; i < n; i++) {
    if (m > vec[i]) {
      sum = findSum(sum, to_string(m - vec[i]));
    } else
      m = vec[i];
  }
  cout << sum;
  return 0;
}
