Shared code

/* 777 */
#include "bits/stdc++.h"
using namespace std;

#define ll long long 

// const int MOD=1e9+7;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	ll n;cin>>n;
	vector<ll>vec(n);
	for(auto &x:vec)cin>>x;
	ll moves=0,maxi=vec[0];
	for(int i=1;i<n;++i){
		moves+=max(0LL,maxi-vec[i]);
		maxi=max(maxi,vec[i]);
	}
	cout<<moves;
}