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

int main()
{
    int n;
    cin>>n;
    set<int> key;
    vector<bool> have;
    have.resize(n+1,false);
    vector<int>room;
    for (int i=0; i<n;i++){
        int x;
        cin>>x;
        room.push_back(x);
    }
    int ans=0;
    while (room[0]!=0){
        key.insert(room[0]);
        have[room[0]]=true;
        ans++;
        room[0]++;
        room[0]=room[0]%n;
    }
    for (int i=1; i<n;i++){
        key.insert((room[i]+ans)%n);
        have[(room[i]+ans)%n]=true;
        if (!have[i]){
            ans++;
            for (auto x:key){
                have[(x+ans)%n]=true;
            }
        }
    }
    cout<<ans;
}