//codeforces
#include <algorithm>
#include <vector>
#include <string>
#include <ctype.h>
#include <set>
#include <map>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<time.h>
#include<string>
#include<stack>
#include<cmath>
#include<iostream>
#include<cstring>
#include<complex>
#include<bitset>
#include<tr1/unordered_set>
#include<tr1/unordered_map>


#define FOR(i,j,k) for(int i=j;i<k;i++)
#define FORD(i,j,k) for(int i=j;i>=k;i--)
#define ll long long
//Make sure no overflow problems
//#define int long long
#define pii  pair<int, int>
#define vi vector<int >
#define pb push_back
#define mp make_pair
#define x first
#define y second
#define VAR(i,n) __typeof(n) i = (n)
#define FOREACH(i,c) for(VAR(i,(c).begin());i!=(c).end();i++)
#define FORDEACH(i,c) for( VAR(i,(c).rbegin()),i!=(c).rend();i++)
#define REP(i,n) FOR(i,0,n)
#define ld long double
const int INF = 1e9+7;
const long long INFLL = (ll)INF * (ll)INF;
const ld EPS = 10e-9;

using namespace std;

class TrieNode{
    public:
    bool isword;
    char c;
    map<char,TrieNode*> m;
    string word;
    public:
    TrieNode(){}
    TrieNode(char ch){
        c=ch;
        isword=false;
    }
};

void insert(TrieNode* root,string word){
    TrieNode* temp=root;
    for(char c:word){
        if(temp->m.find(c)==temp->m.end())
            temp->m[c]=new TrieNode(c);
        temp=temp->m[c];
    }
    temp->isword=true;
    temp->word=word;
}

#pragma GCC optimize ("Ofast")
static auto _ = [] { std::ios::sync_with_stdio(0); std::cin.tie(0); std::cout.tie(0); std::cerr.tie(0); return 0; } ();

int main() {
    stack<int> st;
    int n,k;
    cin>>n;
    long long sum=0;
    for(int i=0;i<n;i++){
        cin>>k;
        if(st.empty())
            st.push(k);
        else if(st.top()>k){
            sum+=(st.top()-k);
        }
        else if(st.top()<k){
            st.push(k);
        }

    }
    cout<<sum;
}




/*
//codechef

#include<bits/stdc++.h> 
#include <algorithm>
#include <vector>
#include <string>
#include <ctype.h>
#include <set>
#include <map>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<time.h>
#include<string>
#include<stack>
#include<cmath>
#include<iostream>
#include<cstring>
#include<complex>
#include<bitset>
#include<tr1/unordered_set>
#include<tr1/unordered_map>


#define FOR(i,j,k) for(int i=j;i<k;i++)
#define FORD(i,j,k) for(int i=j;i>=k;i--)
#define ll long long
//Make sure no overflow problems
//#define int long long
#define pii  pair<int, int>
#define vi vector<int >
#define pb push_back
#define mp make_pair
#define x first
#define y second
#define VAR(i,n) __typeof(n) i = (n)
#define FOREACH(i,c) for(VAR(i,(c).begin());i!=(c).end();i++)
#define FORDEACH(i,c) for( VAR(i,(c).rbegin()),i!=(c).rend();i++)
#define REP(i,n) FOR(i,0,n)
#define ld long double
const int INF = 1000000009;
const long long INFLL = (ll)INF * (ll)INF;
const ld EPS = 10e-9;


#pragma GCC optimize ("Ofast")
static auto _ = [] { std::ios::sync_with_stdio(0); std::cin.tie(0); std::cout.tie(0); std::cerr.tie(0); return 0; } ();

using namespace std; 
void solve(); 
int main() 
{ 

#ifndef ONLINE_JUDGE 
freopen("input.txt", "r", stdin); 
freopen("error.txt", "w", stderr); 
freopen("output.txt", "w", stdout); 
#endif 

int t=1; 
cin>>t; 
while(t--) 
{ 
	solve(); 
	cout<<"\n"; 
} 

cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" secs"<<endl; 
return 0; 
} 
void solve() 
{ 

} 


*/

Measured memory_bytes: 3844