#include 	<iostream>
#include 	<queue>
#include 	<tuple>
#include 	<vector>
#include	<bits/stdc++.h>
#include	<algorithm>
#include 	<cmath>
#include 	<map>
#include 	<string>
#include 	<iomanip> 
#include 	<ctype.h>
#define 	ll  long long int
#define		read(a) long long int a; cin>>a;
#define		in(a) long long int a; cin>>a;
#define 	readstr(s) string s; cin>>s;
#define 	readc(c) char c; cin>>c;
#define 	readarr(a,l) long long int a[l]={0}; for(ll i=0;i<l;i++) cin>>a[i];
#define 	loop(i,a,b) for(ll i=a;i<b;i++)
#define 	rloop(i,a,b) for(ll i=a;i>b;i--)
#define 	loopchar() for(char c='a';c<='z';c++)
#define 	printarr(a, n) fori (i, 1, n) cout << a[i] << " "; cout << endl;
#define		printv(v) for (int i: v) cout << i << " "; cout << endl;
#define 	loopitr(vec) for(auto itr=vec.begin();itr!=vec.end();itr++)
#define 	ff first
#define 	ss second
#define 	readmtrx(i,j,a,b) ll arr[a][b]={0};for(ll i=0;i<a;i++)for(ll j=0;j<b;j++) cin>>arr[i][j];
#define 	time cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n"
#define 	all(a) a.begin(), a.end()
#define 	yes cout <<"YES"<<endl;
#define 	no cout <<"NO"<<endl;
#define 	sc(x) cout << (#x) << " is " << (x) << endl;
#define 	fast ios_base::sync_with_stdio(false);cin.tie(0);
#define 	pb(p) push_back(p)
#define 	mp make_pair
#define 	fsort(vec) sort(vec.begin(),vec.end())
#define 	rsort(vec) sort(vec.begin(),vec.end(),compare)
#define 	endl '\n'
#define 	Endl endl
#define 	setbits(x) __builtin_popcountll(x)
#define 	zrobits(x) __builtin_ctzll(x)
#define 	ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> 
#define 	roundoff std::cout << std::setprecision(15)
#define 	inf 9223372036854775807
#define 	infn -9223372036854775807
#define 	pi 3.14159265358979323846
const 		int mod = 1e9+7; 
#define 	intsize(num) trunc(log10(num)) + 1
#define 	REVERSE(vec) reverse(vec.begin(),vec.end())
using 		namespace std;


ll gcd (ll a, ll b) { return b ? gcd (b, a % b) : a; }
ll lcm (ll a, ll b) { return a / gcd(a, b) * b; }

//code start from here 

//	void constructTree(ll input[], ll segTree[], ll low, ll high, ll pos){
//		if(low==high){
//			segTree[pos]=input[low];
//			return ;
//		}
//		ll mid=(low+high)/2;
//		constructTree(input,segTree,low,mid,2*pos+1);
//		constructTree(input,segTree,mid+1,high,2*pos+2);
//		segTree[pos]=min(segTree[2*pos+1],segTree[2*pos+2]);
//	}

// map<ll,bool>visited;
// map<ll,vector<ll>>adj;

void SieveOfEratosthenes(ll n) 
{  
    bool prime[n+1]; 
    memset(prime, true, sizeof(prime)); 
  
    for (ll p=2; p*p<=n; p++) 
    { 
        if (prime[p] == true) 
        { 
            for (ll i=p*p; i<=n; i += p) 
                prime[i] = false; 
        } 
    } 
    for (ll p=2; p<=n; p++) 
       if (prime[p]) 
          cout << p << " "; 
}
 

vector<ll> prefix_function(string s) {
    ll n = (ll)s.length();
    vector<ll> pre(n);
    for (ll i = 1; i < n; i++) {
        ll j = pre[i-1];
        while (j > 0 && s[i] != s[j])
            j = pre[j-1];
        if (s[i] == s[j])
            j++;
        pre[i] = j;
    }
    return pre;
}


vector<ll>adj[200100];
bool visited[200100];

int main() {
// 	memset(visited,false,sizeof(visited));
	fast;
	 
	read(a)
	readarr(arr,a);
	ll mx=arr[0];
	ll sum=0;
	loop(j,0,a){
		if(arr[j]<=mx){
			sum+=mx-arr[j];
		}
		else{
			mx=arr[j];
		}
	}
	cout<<sum<<endl;
	return 0;
}

//ends here 

Measured memory_bytes: 9896