#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace __gnu_pbds; 
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
using namespace std;
#define ll long long int
#define ld long double
#define ff first
#define ss second  
#define endl '\n'
#define pb push_back
#define t_case ll tt; cin>>tt; while (tt--)
#define all(v) v.begin(),v.end()
#define ub(a,x) upper_bound(all(a),x)-a.begin()
#define lb(a,x) lower_bound(all(a),x)-a.begin()
#define fr(a,b,c) for (ll a=b;a<c;a++)
#define take(xx,n) for (int i=0;i<n;i++) cin>>xx[i];
#define take1(xx,n) for (int i=1;i<=n;i++) cin>>xx[i];
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL);
const auto inf=LLONG_MAX; 
int main() 
{
	fastio
	//t_case
	{
		ll sum=0,f=1,ans=0,n,m=0,z=0,mx=inf,mn=-inf,q;cin>>n;
		ll a[n]; take (a,n);
		for(int i=n-1;i>0;i--) {
		ans+=max(0ll,a[i]-a[i-1]);
		}
		cout<<ans;
		cout<<endl;
	}
	return 0;
}