#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define F0R(i, n) for(int i=0; i<n; i++)
#define FOR(i, a, b) for(int i=a; i<b; i++)
#define ROF(i, a, b) for(int i=b-1; i>=a; i--)
#define siz(x) (int) x.size()
const int mxN = 2e5+10;
int n;
ll a[mxN];
//ll p[mxN], s[mxN];
ll ans = 1e18;
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n;
FOR(i, 1, n+1)
cin >> a[i];
//FOR(i, 2, n+1){
// p[i] = p[i-1]+max(a[i-1]-a[i]+1, 0LL);
//}
//ROF(i, 1, n){
// s[i] = s[i+1]+max(a[i+1]-a[i]+1, 0LL);
//}
// we have some costs on the prefixs and the suffixs
// what to do for the middle element:
// we care about
//FOR(i, 1, n+1){
// // set costs
// ll cur = p[i-1]+s[i+1];
//}
FOR(i, 1, n+1){
priority_queue<ll> sufs, prefs;
//cout << "I: " << i << endl;
FOR(j, 2, i+1){
prefs.push(max(a[j-1]-a[j]+1, 0LL));
//cout << a[j-1]-a[j]+1 << endl;
}
//cout << "---\n";
FOR(j, i, n){
sufs.push(max(a[j+1]-a[j]+1, 0LL));
//cout << a[j+1]-a[j]+1 << endl;
}
ll cur = 0;
while(siz(sufs)&&siz(prefs)){
cur += max(sufs.top(), prefs.top());
sufs.pop(); prefs.pop();
}
while(siz(sufs)) cur += sufs.top(), sufs.pop();
while(siz(prefs)) cur += prefs.top(), prefs.pop();
ans = min(ans, cur);
}
cout << ans << "\n";
}
