#include <iostream>
#include <iosfwd>
#include <iomanip>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <cassert>
#include <cctype>
#include <climits>
#include <vector>
#include <bitset>
#include <set>
#include <queue>
#include <stack>
#include <map>
#include <deque>
#include <string>
#include <list>
#include <iterator>
#include <sstream>
#include <complex>
#include <fstream>
#include <functional>
#include <numeric>
#include <utility>
#include <algorithm>
#include <assert.h>
#include <unordered_map>
using namespace std;
// LIVE AND LET OTHERS LIVE.
#define IOS ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(0);
#define endl '\n'
#define stackofi stack<int>
#define queueofi queue<int>  
#define vectoriterator vector<int>::iterator
#define mapiterator map<int,int>::iterator
#define setiterator set<int>:: iterator
#define yes cout<<"YES"<<endl
#define no cout<<"NO"<<endl
// macros for inputting 1-D and 2-D array.
#define stringiterator string:: iterator
#define pb push_back
#define all(c) (c).begin(),(c).end()
#define rall(c) (c).rbegin(),(c).rend()
#define ai(arr,n) for(int i=0;i<n;i++)cin>>arr[i];
#define ao(arr) for(auto wtf:arr) cout<<wtf<<" ";
#define mi(arr,m,n) for(int i=0;i<m;i++){ for(int j=0;j<n;j++) cin>>arr[i][j];}
#define mo(arr,m,n) for(int i=0;i<m;i++){ for(int j=0;j<n;j++) cout<<arr[i][j]<<" "; cout<<endl;}
#define countsetbits(x) __builtin_popcount(x)
#define ll long long
#define debugger cout<<"I AM EXECUTING"<<endl
#define testcases int asdf; cin>>asdf; while(asdf--)
#define space cout<<endl
#define vi vector<int>
#define si set<int>
#define vc vector<char>
#define sc set<char>
#define vll vector<long long int>
#define vs vector<string>
#define vpp vector<pair<int,int>> 
#define vppo(prs) for(auto x:prs){cout<<x.first<<" "<<x.second<<endl;}
#define For(__,$$,adfdf) for(int __ = $$; __<adfdf;__++)
#define MOD (ll)1e9+7
ll int mpow(ll int base,ll  int exp) {
	base %= MOD;
	ll int result = 1ll;
	while (exp > 0) {
	if (exp & 1ll) result = ((ll)result * base) % MOD;
	base = ((ll)base * base) % MOD;
	exp >>= 1;
	}
	return result;
}
string sconvert(ll int n)
{
	stringstream ss;
	ss<<n;
	string str = ss.str();
	return str;
}
bool sortbysec(const pair<int,int> &a, 
              const pair<int,int> &b) 
{ 
    return (a.second > b.second); 
}
template<typename KeyType, typename ValueType>  // for finding max element in the map.
std::pair<KeyType,ValueType> get_max( const std::map<KeyType,ValueType>& x ) {
  using pairtype=std::pair<KeyType,ValueType>; 
  return *std::max_element(x.begin(), x.end(), [] (const pairtype & p1, const pairtype & p2) {
        return p1.second < p2.second;
  }); 
}

ll int add(ll int a, ll int b, ll int mod = MOD) {
    if (a + b >= mod) {
        return a + b - mod;
    }
    return a + b;
}
 
ll int sub(ll int a,ll int b,ll int mod = MOD) {
    if (a - b < 0) {
        return a - b + mod;
    }
    return a - b;
}
 
ll int mul(ll int a, ll int b, ll int mod = MOD) {
    return (ll int)(1ll * a * b % mod);
}


void  single()
{
	int n;
	cin>>n;
	vi arr(n);
	ai(arr,n);
	ll int answer=0;
	For(i,1,n){
		if(arr[i]<arr[i-1]){
			answer+= arr[i-1]-arr[i];
			arr[i]=arr[i-1];
		}
	}
	cout<<answer<<endl;
	return;
}
void multiple()
{
	testcases
    {
		single();
	}
}

int main()
{
  IOS;
  single();  
  
}















Measured memory_bytes: 3948