#include <bits/stdc++.h>
using namespace std;

int n, vis[100005];

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	cin >> n;
	vector<int> keys;

	int ans = 0;

	for(int i = 0; i < n; ++i){
		int x; cin >> x;

		if(!vis[(x+ans)%n]) keys.push_back((x+ans)%n);
		vis[(x+ans)%n] = 1;

		while(!vis[i]){
			vector<int> nkeys;
			for(int k : keys){
				if(!vis[(k+1)%n]) nkeys.push_back((k+1)%n);
				vis[(k+1)%n] = 1;
			}
			swap(keys, nkeys);
			keys = nkeys;
			++ans;
		}

	}

	cout << ans << '\n';


	return 0;
}