/*MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMWO:,'..'xXWWMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMO. .:kOo.,kNMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMO. .lNWWo..lXMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
MNOxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxMMMMWKxoloxKWNc  .:xxd;  ,dxxxkXMXkxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxMM
MKc''''''''''''''''.  ..'''''.   .''''.  .''MMMWx..,:. .xXo''.  .''.  ..'';kMk;'''''.  .'.''.  .''''''.  ..''.   .''MM
MWNXNNNNNNNNNNNNNNNO' ;KNNNNNKo. cKNNNd. lXNMMMK; ,0Wx. :NWXXl .dNNO' ;KNNNWMWNNNNNXc .kNNNNx. cXNNNNNO' ;KNN0; 'ONNMM
MMMMMMMMMMMMMMMMMWM0' :NMMMMWMX: .OMWWx. oWMMMMWx. ';. .dNMWWo .xMM0' :NWWMMMMMMMMWWl .OMMMWk. lWWMMWM0' ;XMMX: ,KMMMM
MMMMMMWMWkccccccccc;. :NMWNNNKd. :XMMWx. oWMMMWKo. .',. .,ldx; .dMM0' :NMMMMMMMNNWMWl .OMMMWk. lWMMMMM0' ;XMMX: ,0MMMM
MMWXKNWMWxcc,. .;cc;. :XMk,''..'lKWMMWx. oWMNx:. .lONNKxl.     .xMM0' :NMMMMMM0:,oKO' ,KMMMMk. lWWNkoc,. .;::;. ,KMMMM
MMXc.lXMMWWWNd..xWM0' :NM0;  ;kXWMMMWNl  oWMK:.;xXWWMWXx:. ,c' .dMM0' :NMMMMMMKc. ...;kWMMMMk. lWWc .:;. .clc:. ,KMMMM
MWWx. lXMWMMMK, lWM0' :NMMNx'.,ldxxoc'   oWMWNKNWWWN0o' .:kNWo .dMM0' :NMMMMMMMNO;  ,OWWWMMMk. lWM' lXx. lNMMX: ,KMMMM
MMMWk'.,xKNX0c..kWM0' :NMMMMNkl;,'',:l:  oWMMMMMWMWO' 'l0WMWWo .xMM0' :NMMMMMMMMMNd. .oXWMMMk. lWMd.....;0WMMX: ,KMMMM
MMMMWKo'...'..:kWMM0' :NMMMMMMMWWNNWWWx. oWMMMMMMMMWOxXWMWMWWo .xMM0' :NMMMMMMMMMMMKl. ,kNMMk. lWMWKkxx0NMWMMX: ,KMMMM
MMMMMMMN0kxk0XNWMMWKl;xNMMMMMMMMMMMMWM0c;kWMMMMMMMMMMMWWMMMMWk;:OMMXl,dNMMMMMMMMMMMMWO; .dNM0c;kWWMMMMMMMMMMMNd,oXMMMM
MMMMMMMMWWMWMMMMMMMMMWWMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMWWMMWWMMWMMMMMMMMMMMMMMNkxKWMMWWMMMMMMMMMMMMMMWMMWMMMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM*/

//             Author: Udit "luctivud" Gupta @ (https://www.linkedin.com/in/udit-gupta-1b7863135/)                  //


#include <bits/stdc++.h>
#pragma GCC optimize "trapv"

using namespace std;

typedef long long int lld;
typedef unsigned long long int llu;

#define         TESTCASES()    cin >> (T3X0); T353 = T3X0; while(T3X0--)
#define         _input(V3C)    for(auto &V3C_I7 : (V3C)) cin >> (V3C_I7)
#define   mems(A77AY, V4LU)    memset((A77AY), (V4LU), sizeof((A77AY)))
#define    CH3K(I7, E4, S7)    (((S7)<0) ? (I7)>(E4) : (I7)<(E4))
#define   for4(I7,S4,E4,S7)    for(auto I7=(S4); CH3K(I7,E4,S7); (I7)+=(S7))
#define              len(v)    ((int)((v).size()))
#define              all(x)    (x).begin(), (x).end()
#define             rall(x)    (x).rbegin(), (x).rend()
#define             deb1(x)    cout << #x << "=" << (x) << "\n";
#define             deb2(x)    cout << #x << "=" << (x) << " ";



void solveEachTest(lld T35TC453N = 1) {
	lld n; cin >> n;
	vector<lld> arr(n);
	_input(arr);
	lld maxsofar = arr[0], ans = 0ll;

	for4(i, 1ll, n, 1ll) {
		ans += max(0ll, maxsofar - arr[i]);
		maxsofar = max(maxsofar, arr[i]);
	}

	cout << ans;



	cout << "\n";

	return;
}


signed main() {
	ios_base::sync_with_stdio(false); cin.tie(0); cout.precision(10);

	lld T3X0 = 0, T353 = 1;

	// TESTCASES()
	solveEachTest(T353 - T3X0);
	return 0;
}
// Random Thought :  null

Measured memory_bytes: 4724