#include<bits/stdc++.h>
using namespace std;
#define int long long
#define in pair<int, int>
#define f first
#define s second
#define pb push_back
#define pob pop_back
#define INF (int)1e17
#define MX (int)3e5+5
#define fast() ios_base::sync_with_stdio(false); cin.tie(NULL)
signed main()
{
fast();
int n;
cin >> n;
vector<int> a(n);
for(int i = 0; i < n; i++)
cin >> a[i];
for(int i = n-1; i > 0; i--)
a[i]-=a[i-1];
vector<int> pref(n), suff(n+1);
pref[0] = 0;
for(int i = 1; i < n; i++)
{
pref[i] = pref[i-1];
if(a[i] > 0)
continue;
pref[i]+=(1-a[i]);
}
suff[n] = 0;
for(int i = n-1; i > 0; i--)
{
suff[i] = suff[i+1];
if(a[i] < 0)
continue;
suff[i]+=(1+a[i]);
}
int ans = INF;
for(int k = 1; k <= n; k++)
ans = min(max(pref[k-1], suff[k]), ans);
cout << ans << "\n";
return 0;
}
