#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define int long long
#define yes() cout << "YES\n"
#define no() cout << "NO\n"
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
const int inf = 1e18;
const int mod = 1e9 + 7;
const int maxn = 3e5;
const int mod1 = 998244353;
const int mod2 = 1e18 + 1;
const int mod3 = 1e9 + 9;
const int mod4 = 333333333;
const int mod5 = 200000;
const int mod6 = 10007;
const int k = 3000;
const int w = 1e5;
const ld EPS = 1e-8;
int LOG = 30;
void solve() {
int n;
cin >> n;
vector<int> a(n);
for (int& i : a) cin >> i;
vector<int> b(n);
b[0] = a[0];
for (int i = 1; i < n; i++) b[i] = a[i] - a[i - 1];
int ans = inf;
for (int i = 0; i < n; i++) {
int cur = 0;
int res = 0;
for (int j = 0; j <= i; j++) if (b[j] <= 0) {
cur += (-b[j] + 1);
res += (-b[j] + 1);
}
for (int j = i + 1; j < n; j++) {
if (b[j] >= 0) {
int x = b[j] + 1;
if (cur >= x) cur -= x;
else {
res += x - cur;
cur = 0;
}
}
}
ans = min(ans, res);
}
cout << ans << "\n";
}
signed main() {
#ifdef LOCAL
#else
// freopen("qual" ".in", "r", stdin);
// freopen("qual" ".out", "w", stdout);
#endif
// cout.precision(16);
ios::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
