#include<bits/stdc++.h>
using namespace std;
#define all(fl) fl.begin(),fl.end()
#define pb push_back
#define fi first
#define se second
#define for1(i,j,k) for(int i=j;i<=k;i++)
#define for2(i,j,k) for(int i=j;i>=k;i--)
#define for3(i,j,k,l) for(int i=j;i<=k;i+=l)
#define lb lower_bound
#define ub upper_bound
#define sz(a) (int)a.size()
#define pii pair<int,int>
#define pli pair<long long,int>
#define gcd __gcd
#define lcm(x,y) x*y/__gcd(x,y)
#define pil pair<int,long long>
const int maxn=2e5+9;
long long a[maxn],b[maxn],c[maxn];
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
//freopen("temp.INP","r",stdin);
//freopen("temp.OUT","w",stdout);
int n;
cin>>n;
for1(i,1,n)cin>>a[i];
for1(i,2,n){
b[i]=b[i-1]+max(0ll,a[i-1]-a[i]);
if (a[i-1]>=a[i])b[i]++;
}
for2(i,n-1,1){
c[i]=c[i+1]+max(0ll,a[i+1]-a[i]);
if (a[i+1]>=a[i])c[i]++;
}
long long ans=1e18;
for1(i,1,n){
ans=min(ans,b[i]+c[i]-min(b[i],c[i]));
}
cout<<ans;
}
