#include <bits/stdc++.h>
#define ll long long
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
ll n;
cin >> n;
vector<ll> a(n);
for (int i=0; i<n; i++) {
cin >> a[i];
}
vector<ll> diff(n);
diff[0] = a[0];
for (int i=0; i<n-1; i++) {
diff[i+1] = a[i+1]-a[i];
}
vector<ll> pref(n+1);
for (int i=0; i<n; i++) {
pref[i] = (i>0 ? pref[i-1] : 0) + (diff[i]<=0 ? abs(diff[i])+1 : 0);
}
vector<ll> suff(n+1);
for (int i=n-1; i>=0; i--) {
suff[i] = suff[i+1]+(diff[i]>=0 ? abs(diff[i])+1 : 0);
}
ll res = 1e18;
for (int i=0; i<n; i++) {
res = min(res, max(suff[i+1], pref[i]));
}
cout << res;
}
