#include <fstream>
using namespace std;

ifstream f("operatii.in");
ofstream g("operatii.out");

unsigned int n, a, b, sol, mx, scad;
int main()
{
    f >> n;
    for (int i = 1; i <= n + 1; ++i)
    {
        if (i == n + 1) a = 0;
        else
            f >> a;
        if (a >= b)
        {
            if (mx < a) mx = a;
        }
        else
        {
            sol = sol + mx - scad;
            scad = a;
            mx = a;
        }
        b = a;
    }


    g << sol << '\n';
    g.close();
    return 0;
}