#include <bits/stdc++.h>
using namespace __gnu_cxx;
using namespace std;
#define LL long long
#define pLL pair<long long, long long>
#define F first
#define S second
#define pb push_back
#define rz resize
#define all(x) x.begin(), x.end()
void Star_Brust_Stream()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
return;
}
const LL INF = 1e18;
const LL mod = 1e9 + 7;
LL f(LL a, LL b, LL m)
{
LL c = 1;
for (; b > 0; b >>= 1)
{
if (b & 1)
{
c = (c * a) % m;
}
a = (a * a) % m;
}
return c % m;
}
LL m(LL a, LL b)
{
a += ((-a / b) + 2) * b;
return a % b;
}
int main()
{
Star_Brust_Stream();
LL n;
cin >> n;
vector<LL> v(n);
for (int i = 0; i < n; i++)
{
cin >> v[i];
}
LL ans = 1e18;
for (int i = 0; i < n; i++)
{
LL cnt = 0;
for (int j = 0; j < i; j++)
{
if (v[j] >= v[j + 1])
{
cnt += (v[j] - v[j + 1] + 1);
}
}
v[i] += cnt;
for (int j = i; j < n; j++)
{
if (v[j] <= v[j + 1])
{
cnt += (v[j + 1] - v[j] + 1);
}
}
ans = min(ans, cnt);
}
cout << ans << endl;
// system("pause");
return 0;
}
