
#include <bits/stdc++.h>
#define ll long long int
#define all(x) x.begin(), x.end()
using namespace std;
ll power(ll x, ll y,ll  m) 
{ 
    if (y == 0) 
        return 1; 
    ll  p = power(x, y/2, m) % m; 
    p = (p * p) % m; 
  
    return (y%2 == 0)? p : (x * p) % m; 
} 
ll modInverse(ll a, ll m) 
{ 
    ll g = __gcd(a, m); 
    if (g != 1) 
        cout << "Inverse doesn't exist"; 
    
    
        // If a and m are relatively prime, then modulo inverse 
        // is a^(m-2) mode m 
        
              return power(a, m-2, m); 
    
} 
ll fact[1000];
void fac(ll m)
{
	ll i;
	fact[0]=1;
	for(i=1;i<1000;i++)
	{
		fact[i]=(i*fact[i-1])%m;
	}
}

ll comb(ll n,ll k,ll m)
{
	return(fact[n]*modInverse(fact[k],m)%m *modInverse(fact[n-k],m)%m)%m;
}
bool cmp(pair<ll,ll> a,pair<ll,ll>b)
{
	if(a.second==b.second)
	return a.first<b.first;
	return a.second>b.second;
}
int main () {
ios_base::sync_with_stdio(false);
    cin.tie(NULL);
  ll n;
  cin>>n;
  ll i;
  ll a[n];
  for(i=0;i<n;i++)
  cin>>a[i];
  ll ans;
  ll m=a[0];
  for(i=1;i<n;i++)
  {
  	if(a[i]>=m)
  	{
  		m=a[i];
	  }
	  else
	  {
	  	ans+=m-a[i];
	  }
  }
cout<<ans<<endl;
return 0;
}
