#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n';
const int M = 1e5+5, MOD = 1e9+7;
signed main() {
cin.tie(0)->sync_with_stdio(0);
int n;
cin >> n;
vector<int> v(n);
for (int &i:v) cin >> i;
vector<int> x;
for (int i = 1; i < n; i++) x.push_back(v[i]-v[i-1]);
int a = 0, b = 0, ans = INT_MAX;
for (int i:x) if (i >= 0) a+=i+1;
for (int i = 0; i < n; i++) {
if (i) {
if (x[i-1] >= 0) a -= x[i-1]+1;
if (x[i-1] <= 0) b -= x[i-1]-1;
}
ans = min(ans, max(a, b));
} cout << ans << endl;
return 0;
}
/*
8
12 2 34 85 4 91 29 85
-11 33 52 -82 88 -63 57
5
9 7 5 3 1
-2 -2 -2 -2
5
3 2 2 3 1
*/
