#include <iostream>
using namespace std;
const int N = 100010;
int price[N];
int n;
int main()
{
scanf("%d", &n);
for (int i = 0; i < n; i ++ ) scanf("%d", &price[i]);
int res = 0;
for (int i = 0; i + 1 < n; i ++ ) //只要后一天比前一天价格高,就卖出
{
int dt = price[i + 1] - price[i];
if (dt > 0)
res += dt;
}
printf("%d", res);
return 0;
}