#include<bits/stdc++.h>
using namespace std;
const int MaxN = 1e6 + 5;
long long n, a[MaxN];
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    freopen("file.inp", "r", stdin);
    freopen("file.out", "w", stdout);
   cin >> n;

    long long mx = 0;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        mx = max(mx, a[i]);
    }

    long long res = mx - a[1];
    for (int i = 2; i <= n; i++)
    {
        res += max(0LL, a[i - 1] - a[i]);
    }

    cout << res << "\n";

    return 0;
}