#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream cin ("operatii.in");
    ofstream cout ("operatii.out");
    int n, v[100000];
    cin >> n;
    for (int i=1; i<=n; i++)
        cin >> v[i];
    int s = 0;
    for (int i=1; i<=n-1; i++)
        if (v[i] <= v[i+1])
            s += v[i]-v[i+1];
    if (s < 0)
        s *= -1;
    cout << s;
    return 0;
}