#pragma region Macros
#include <bits/stdc++.h>
using namespace std;
// iteration helper
#define FOR(i, l, r) for (int i = (l); i < (r); ++i)
#define REP(i, n) FOR(i, 0, n)
#define RFOR(i, l, r) for (int i = (r)-1; i >= (l); --i)
#define RREP(i, n) RFOR(i, 0, n)
#define EACH(i, c) for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e) != (s).end())
#define PB push_back
// MyVector
template <typename T>
class MyVector : private std::vector<T, std::allocator<T>>
{
public:
	using basetype = std::vector<T, std::allocator<T>>;
	using basetype::vector; // constractor
	using basetype::operator=;
	using basetype::begin;
	using basetype::capacity;
	using basetype::cbegin;
	using basetype::cend;
	using basetype::crbegin;
	using basetype::crend;
	using basetype::empty;
	using basetype::end;
	using basetype::max_size;
	using basetype::rbegin;
	using basetype::rend;
	using basetype::reserve;
	using basetype::resize;
	using basetype::shrink_to_fit;
	using basetype::size;

	// []のかわりに at をつかう
	typename MyVector<T>::reference operator[](typename basetype::size_type n) { basetype::at(n); }
	typename MyVector<T>::const_reference operator[](typename basetype::size_type n) const { basetype::at(n); };

	using basetype::assign;
	using basetype::at;
	using basetype::back;
	using basetype::clear;
	using basetype::data;
	using basetype::emplace;
	using basetype::emplace_back;
	using basetype::erase;
	using basetype::front;
	using basetype::insert;
	using basetype::pop_back;
	using basetype::push_back;
	using basetype::swap;
};
#ifdef _DEBUG
#define vector MyVector
#else
#define vector std::vector
#endif
// typedefs
#define ll long long
#define vi vector<int>
#define vi2 vector<vi>
// input
#define ci(x) \
	int x;    \
	cin >> x
#define cs(x) \
	string x; \
	cin >> x
#define cd(x) \
	double x; \
	cin >> x
#define cvi(x, n) \
	vi x(n);      \
	REP(i, n) { cin >> x[i]; }
// const input
#define cci(x) const int x = []() {int t;cin>>t;return t; }()
#define ccs(x) const string x = []() {string t;cin>>t;return t; }()
#define ccd(x) const double x = []() {double t;cin>>t;return t; }()
// output
#define pr(x) cout << x << endl
#define prvec(v)     \
	REP(i, v.size()) \
	pr(v[i])
#define ppr(x) cout << x
#define lf() cout << endl
// debug methods
// usage: debug(x,y);
#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cout << #x1 << ": " << x1 << endl
#define debug_2(x1, x2) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << endl
#define debug_4(x1, x2, x3, x4) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5) cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#ifdef _DEBUG
#define debug(...)                                                        \
	CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~)) \
	(__VA_ARGS__)
#else
#define debug(...)
#endif
// const number
const double PI = acos(-1.0);
const double EPS = 1e-10;

int powint(int a, int x)
{
	int res = 1;
	REP(i, x)
	{
		res = res * a;
	}
	return res;
}
#pragma endregion
#define int long long
signed main()
{
#ifdef _DEBUG
	try
	{
#endif
		// main program ---------------------------------------------
		cci(N);
		vi A(N);
		REP(i, N)
		{
			cin >> A[i];
		}
		int ans = 0;
		REP(i, N)
		{
			if (i == 0)
				continue;
			if (A[i] < A[i - 1])
			{
				ans += A[i - 1] - A[i];
				A[i] = A[i - 1];
			}
		}
		pr(ans);
// end main program -----------------------------------------
#ifdef _DEBUG
	}
	catch (std::out_of_range &ex)
	{
		pr("out of range");
	}
#endif
	return 0;
}


Measured memory_bytes: 4784