#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
#define ll long long
#define int long long
#define pb push_back
#define fi first
#define se second
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
#define ld long double
using namespace std;
typedef pair<int,int> pii;
typedef pair<pii, int> ipii;
const int MAXN = 2e5+10;
const int MAXA = 2e3+10;
const int INF = 1e18+10;
const int LOG = 29;
const int MOD = 1e9+7;
const int SQRT = 450;
const vector<int> NOL = {};
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const vector<int> dx = {1, -1, 0, 0};
const vector<int> dy = {0, 0, 1, -1};
int n;
int a[MAXN];
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n;
for(int i=1; i<=n; i++) cin >> a[i];
int ANS = INF;
for(int i=1; i<=n; i++){
int le = 0, ri = 0;
for(int j=1; j<=i-1; j++){
if(a[j-1] < a[j]) continue;
le += a[j-1]-a[j]+1;
}
for(int j=n; j>=i+1; j--){
if(a[j+1] < a[j]) continue;
ri += a[j+1]-a[j]+1;
}
int l = a[i-1]+le, r = a[i+1]+ri;
int te = a[i]+max(le, ri);
int cost = 0;
if(te <= max(l, r)) cost = max(l, r)-te+1;
// cout << i << ' ' << le << ' ' << ri << ' ' << cost << " pp\n";
ANS = min(ANS, cost+max(le, ri));
}
cout << ANS << '\n';
}
