#pragma GCC optimze("Ofast")
#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define mod 1000000007
#define md 998244353
#define trace(...)
#define ll long long int
#define ld long double
#define fi first
#define se second
#define fr(i,a,b) for(ll i=a;i<=b;i++)
#define frr(i,b,a) for(ll i=b;i>=a;i--)
#define mem(a) memset(a, 0, sizeof(a))
#define vpi std::vector<pair<int,int>>
#define pii pair<int,int>
#define pb push_back
#define sall(v) sort(v.begin(),v.end())
#define all(v) (v.begin(),v.end())
#define minf -10000000
#define vi vector<int>
const ll infl=0x3f3f3f3f3f3f3f3fLL;
const int infi=0x3f3f3f3f;
typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> oset;
auto clk=clock();
mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
int rng(int lim) {
    uniform_int_distribution<int> uid(0,lim-1);
    return uid(rang);
}
ll power(ll x, ll y,ll p) { 
    ll res = 1;      
    x = x % p;  
    while (y > 0) {  
        if (y & 1){  
            res = (res*x) % p;  
        }
        y = y>>1;
        x = (x*x) % p;   
    } 
    return res; 
}
ll power(ll x, ll y) { 
    ll res = 1;       
    while (y > 0) {    
        if (y & 1) 
            res = (res*x) ;  
        y = y>>1; 
        x = (x*x);   
    } 
    return res; 
}
 
ll max3(ll a,ll b,ll c){
    return max(a,max(b,c));
}
ll min3(ll a,ll b,ll c){
    return min(a,min(b,c));
}
bool isPrime(ll n) { // Corner cases 
    if (n <= 1) 
        return false; 
    if (n <= 3) 
        return true; 
    if (n % 2 == 0 || n % 3 == 0) 
        return false; 
    for (ll i = 5; i * i <= n; i = i + 6) 
        if (n % i == 0 || n % (i + 2) == 0) 
            return false; 
    return true; 
}
const int nax=2e5+5;
void solve(){
    int n;cin>>n;
    vector<ll> v(n);fr(i,0,n-1)cin>>v[i];
    ll cnt=0,mx=v[0];
    fr(i,1,n-1){cnt+=max(0ll,mx-v[i]);mx=max(mx,v[i]);}
    cout<<cnt<<endl;
    return;
}

int main(){
    ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    srand(chrono::high_resolution_clock::now().time_since_epoch().count());
    cout<<fixed<<setprecision(8);
    #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    #endif
    int t;
    // cin>>t;
    t=1;
    while(t--){
        solve();
    }
    #ifndef ONLINE_JUDGE
    cout<<endl<<endl<<endl<<endl<<"Time elapsed: "<<(double)(clock()-clk)/CLOCKS_PER_SEC<<endl;
    #endif
    return 0;
}
#include <iostream>
#define ll long long
using namespace std;
int main () {
	int q,p = 0,n; cin >> q; ll ans = 0;
	while (q--){
		cin >> n;
		if (n<p) ans += p-n;
		else p=n;
	} cout << ans << "\n";
	return 0;
}