#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, steps;
  int A[2] = {0, 0};
  N = 0;
  steps = 0;
  cin >> N;
  if (1 <= N && N <= 2 * 100000) {
    for (int i = 0; i < N; i++) {
      cin >> A[1];
      if (A[1] - A[0] < 0) {
        steps += A[0] - A[1];
      } else if (A[1] - A[0] > 0) {
        A[0] = A[1];
      }
    }
  }
  cout << steps << endl;
  return 0;
}
