#include<bits/stdc++.h>
using namespace std;
int n;
const int N = 1e5 + 117;
int a[N];
int maxn = 0;
int ans = 0;
int main() {
	cin >> n;
	for(int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	int i = 1;
	while(i <= n) {
		int j = i;
		while(a[j] >= a[j + 1]){
			j++;
		}
		ans += a[i] - a[j];
//		cout << i << ' ' << j << endl;
		i = j + 1;
	}
	cout << ans;
	return 0;
}