#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 5e5 + 9;
int a[N];
int l[N];
int r[N];
int ans = 0;
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
int n;cin>>n;
for(int i=1;i<=n;i++) cin>>a[i];
int mid = a[1];
for(int i=2;i<=n;i++){
if(mid<a[i]) mid = a[i];
l[i] = mid;
}
mid = a[n];
for(int i=n-1;i>=1;i--){
if(mid<a[i]) mid = a[i];
r[i] = mid;
}
for(int i=1;i<=n;i++){
if(a[i]<min(l[i],r[i])) ans+=min(l[i],r[i])-a[i];
}
cout<<ans;
}