#include <bits/stdc++.h>

using namespace std;

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

const int NMAX = 1000005;
int n, v[NMAX];
long long ans;

int main(){
    int i,lo,hi;
    f >> n;
    for(i = 1 ; i <= n ; i++)
        f >> v[i];

    int value = v[1];
    for(i = 1 ; i <= n + 1 ; i++)
        if(v[i] > value){
            value = v[i];
        }else
            if(v[i] < value){
                ans += value - v[i];
                value = v[i];
            }

    g << ans;


    return 0;
}