#include <bits/stdc++.h>
#define bigdata ios::sync_with_stdio(false);cin.tie(nullptr)
using namespace std;
typedef long long ll;

const int INF = 1E9 + 7;
int n;
vector<int> a;
int main(){
    bigdata;
    cin >> n;
    a.resize(n);
    int maxpoint = 0;
    int maxh = 0;
    for (int i = 0; i < n; ++i){
        int tmp;
        cin >> tmp;
        a[i] = tmp;
        if (tmp > maxh){
            maxh = tmp;
            maxpoint = i;
        }
    }
    int curmax = 0;
    int left = 0;
    for (int i = 0; i < maxpoint; ++i){
        if (a[i] >= curmax){
            curmax = a[i];
        }
        else{
            left += curmax - a[i];
        }
    }
    int right = 0;
    curmax = 0;
    for (int i = n - 1; i > maxpoint; --i){
        if (a[i] >= curmax){
            curmax = a[i];
        }
        else{
            right += curmax - a[i];
        }
    }
    cout << left + right;
}