#include <bits/stdc++.h>
using namespace std;

// TYPEDEF
// ----------------------------------------
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> Pair;
typedef vector<ll> vll;
typedef vector<vector<ll>> Graph;
typedef vector<string> vs;
typedef vector<pair<ll, ll>> Pll;
typedef queue<ll> qll;

// REPEAT
// ----------------------------------------
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define REPD(i,n) for(ll i=n-1;i>=0;i--)
#define REPA(i,a) for(ll i=0;i<(ll)(a.size());i++);
#define FOR(i,a,b) for(ll i=a;i<=(ll)(b);i++)
#define FORD(i,a,b) for(ll i=a;i>=(ll)(b);i--)
#define COUT(a) cout << (a) << endl;
#define ENDL(a) cout << endl;
#define COUTA(i,a) for(ll i=0;i<(ll)(a.size());i++) {cout << (a)[i] << " ";} cout << endl;

// UTIL
// ----------------------------------------
#define pb push_back
#define paired make_pair
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define RSORT(a) sort((a).rbegin(), (a).rend())

// PRINT
// ----------------------------------------
#define YES cout << "YES" << endl;
#define NO cout << "NO" << endl;
#define Yes cout << "Yes" << endl;
#define No cout << "No" << endl;

// DEBUG
// ----------------------------------------
#ifdef _DEBUG
#define debug(x) cout << "[debug] " << #x << ": " << x << endl
#else
#define debug(x)
#endif

template <typename T>
void debugV(const vector<T> v) {
#ifdef _DEBUG
  rep(i, v.size()) {
    cout << i << ":" << v[i] << " ";
  }
  cout << endl;
#else
  (void)v;
#endif
}

// BIT FLAG
// ----------------------------------------
const unsigned int BIT_FLAG_0 = (1 << 0); // 0000 0000 0000 0001
const unsigned int BIT_FLAG_1 = (1 << 1); // 0000 0000 0000 0010
const unsigned int BIT_FLAG_2 = (1 << 2); // 0000 0000 0000 0100
const unsigned int BIT_FLAG_3 = (1 << 3); // 0000 0000 0000 1000
const unsigned int BIT_FLAG_4 = (1 << 4); // 0000 0000 0001 0000
const unsigned int BIT_FLAG_5 = (1 << 5); // 0000 0000 0010 0000
const unsigned int BIT_FLAG_6 = (1 << 6); // 0000 0000 0100 0000
const unsigned int BIT_FLAG_7 = (1 << 7); // 0000 0000 1000 0000
const unsigned int BIT_FLAG_8 = (1 << 8); // 0000 0001 0000 0000
const unsigned int BIT_FLAG_9 = (1 << 9); // 0000 0010 0000 0000
const unsigned int BIT_FLAG_10 = (1 << 10); // 0000 0100 0000 0000
const unsigned int BIT_FLAG_11 = (1 << 11); // 0000 1000 0000 0000

// CONST
// ----------------------------------------
constexpr ll INF = 0x3f3f3f3f3f3f3f3f;
constexpr double PI=3.14159265358979323846; // or M_PI
constexpr int MOD = 1000000007;


struct UnionFind {
  vll data;
 
  UnionFind(ll sz) {
    data.assign(sz, -1);
  }
 
  bool unite(ll x, ll y) {
    x = find(x);
    y = find(y);
    if (x == y) {
      return (false);
    }
    if (data[x] > data[y]) {
      swap(x, y);
    }
    data[x] += data[y];
    data[y] = x;
    return (true);
  }
 
  ll find(ll k) {
    if(data[k] < 0) {
      return (k);
    }
    return (data[k] = find(data[k]));
  }
 
  ll size(ll k) {
    return (-data[find(k)]);
  }

  ll same(ll x, ll y) {
    return (find(x) == find(y));
  }
};



void Main() {
  ll n;
  cin >> n;

  ll count = 0;
  vll a(n);
  REP(i, n) {
    cin >> a[i];
  }
  FOR(i, 1, n - 1) {
    if (a[i - 1] > a[i]) {
      ll daiza = a[i - 1] - a[i];
      count += daiza;
      a[i] += daiza;
    }
  }
  COUT(count);
}

int main()
{
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(15);
	Main();
}

/*

5
2 1 5 4 3
*/


Measured memory_bytes: 4776