#include <bits/stdc++.h>
using namespace std;
using lint = long long;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int N;
cin >> N;
vector<lint> A(N);
for (int i = 0; i < N; i++) {
cin >> A[i];
}
vector<lint> B(N - 1);
for (int i = 0; i < N - 1; i++) {
B[i] = A[i + 1] - A[i];
}
// [l, r] += v -> B[l - 1] += v, B[r] -= v
// exist k, B[0...k-1] >= 1, B[k...N-2] <= -1
vector<lint> pref(N - 1);
vector<lint> suff(N - 1);
for (int i = 0; i < N - 1; i++) {
pref[i] = (i > 0 ? pref[i - 1] : 0) + (B[i] <= 0 ? (-B[i] + 1) : 0);
}
for (int i = N - 2; i >= 0; i--) {
suff[i] = (i < N - 2 ? suff[i + 1] : 0) + (B[i] >= 0 ? (B[i] + 1) : 0);
}
lint ans = LLONG_MAX;
for (int i = 0; i < N; i++) {
ans = min(ans, max(i > 0 ? pref[i - 1] : 0, i < N - 1 ? suff[i] : 0));
}
cout << ans << '\n';
return 0;
}
