#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define ll long long
#define pb push_back
#define mp make_pair
bool isPrime(ll n) 
{ 
    
    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; 
} 
ll minthis(ll a, ll b){
if(a < b){
return a;
}
return b;
}
ll maxthis(ll a, ll b){
if(a > b){
return a;
}
return b;
}
int gcd(int a, int b){
    if( a<0 ) a = -a;
    if( b<0 ) b = -b;
    while( b!=0 ){
        a %= b;
        if( a==0 ) return b;
        b %= a;
    }
    return a;
}
 
int findLargestDivisor(int n) 
{ 
	int max = 1;
    for (int i = 2; i < n; i++) {        
        if(n %(i) == 0) { 
            max = i;
        } 
    }
    return max;     
} 
 
 
ll power(ll x, ll y)  
{  
    ll temp;  
    if(y == 0)  
        return 1;  
    temp = power(x, y / 2);  
    if (y % 2 == 0)  
        return temp * temp;  
    else
    {  
        if(y > 0)  
            return x * temp * temp;  
        else
            return (temp * temp) / x;  
    }  
} 

void solve(){	
  int n;
cin >> n;
int arr[n+1] = {};
arr[n] = INT_MAX;
for(int i = 0 ; i < n ; i++){
    cin >> arr[i];
}
int ans = 0;
for(int i = 0 ; i < n; i++){
    if(arr[i] > arr[i+1]){
        ans += abs(arr[i]-arr[i+1]);
        arr[i+1] = arr[i];
    }   
}
cout << ans << "\n";
}
 
int main(){ 
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int t = 1;
    //cin >> t;
    while(t--){
	solve();
    }
    return 0; 
}

