#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define st first
#define nd second
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define debug false
const int MAXN = 200 * 1000;
ll a[MAXN];
int main () {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n;
cin >> n;
for (int i = 0; i < n; i ++) {
cin >> a[i];
}
int ind = 0;
int rekord = 0;
for (int i = 0; i < n; i ++) {
if (a[i] > rekord) {
rekord = a[i];
ind = i;
}
}
ll w1 = 0, w2 = 0;
for (int j = ind; j < n - 1; j ++) {
w2 += max(0LL, a[j + 1] - a[j] + 1LL);
}
for (int j = 0; j < ind; j ++) {
w1 += max(0LL, a[j] - a[j + 1] + 1LL);
}
cout << max(w1, w2) << "\n";
return 0;
}
