#include <bits/stdc++.h>
using namespace std;

int main(){
          int sum = 0;
          int n; cin >> n;
          int a[n];
           for(int i=0; i<n; ++i) { cin >> a[i]; }
           for(int i =0; i<n; ++i){
                  if(a[i] >a[i+1) sum += a[i] - a[i-1];
           }
         cout << sum;
       return 0;
}