#include<iostream>
#include<fstream>
using namespace std;
int st[1000004],i,nr,n,x;
long long sol;
int main()
{

    ifstream cin("operatii.in");
    ofstream cout("operatii.out");
    cin>>n;
    for(i=1;i<=n+1;i++)
    {
        if(i<=n)
            cin>>x;
        else x=0;
        if(i==1)
        {

            nr++;
            st[nr]=x;
            continue;
        }

        if(x>st[nr])
        {

            nr++;
            st[nr]=x;
        }
        if(x<st[nr])
        {
            sol=(long long) sol + st[nr] - x;
            nr--;
            while(x<st[nr]&&nr>0)
                nr--;
            nr++;
            st[nr]=x;

        }

    }
    cout<<sol;
    return 0;
}