#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using namespace std;
template <typename T>
inline bool read(T& ret) {
  T x = 0, f = 1;
  char ch = getchar();
  while (ch != EOF && (ch > '9' || ch < '0')) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  if (EOF == ch) return false;
  do x = x * 10 + ch - 48, ch = getchar();
  while (ch >= '0' && ch <= '9');
  ret = x * f;
  return true;
}
inline char nc() {
  static char buf[100000], *p1 = buf, *p2 = buf;
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
template <typename T>
bool rn(T& v) {
  static char ch;
  while (ch != EOF && !isdigit(ch)) ch = nc();
  if (ch == EOF) return false;
  for (v = 0; isdigit(ch); ch = nc()) v = v * 10 + ch - '0';
  return true;
}
template <typename T>
void o(T p) {
  static int stk[70], tp;
  if (p == 0) {
    putchar('0');
    return;
  }
  if (p < 0) {
    p = -p;
    putchar('-');
  }
  while (p) stk[++tp] = p % 10, p /= 10;
  while (tp) putchar(stk[tp--] + '0');
}
LL bin(LL x, LL n, LL MOD) {
  LL ret = MOD != 1;
  for (x %= MOD; n; n >>= 1, x = x * x % MOD)
    if (n & 1) ret = ret * x % MOD;
  return ret;
}
inline LL get_inv(LL x, LL p) { return bin(x, p - 2, p); }
void Solve() {}
int A[200010];
int main() {
  int N;
  while (cin >> N) {
    int ans = 0;
    for (int i = 0; i < N; i++) {
      cin >> A[i];
    }
    int pre = A[0];
    for (int i = 1; i < N; i++) {
      if (A[i] >= pre) {
        pre = A[i];
      } else {
        ans += (pre - A[i]);
      }
    }
    cout << ans << endl;
  }
  return 0;
  return 0;
}
