#include<bits/stdc++.h>
using namespace std;
int main(){
int n, mn = (int)1e9, ans;
cin >> n;
int a[n];
vector<int> pos(n);
vector<int> neg(n);
for(int i = 0; i < n; i++) cin >> a[i];
for(int i = 1; i < n; i++){
if(a[i] > a[i-1]){
pos[i] = pos[i-1];
neg[i] = neg[i-1] + a[i] - a[i-1] + 1;
}
else if(a[i] < a[i-1]){
pos[i] = pos[i-1] + a[i-1] - a[i] + 1;
neg[i] = neg[i-1];
}
else{
pos[i] = pos[i-1] + 1;
neg[i] = neg[i-1] + 1;
}
}
for(int k = 0; k < n; k++){
ans = pos[k] + neg[n-k-1];
mn = min(mn,ans);
}
cout << mn << endl;
return 0;
}
