#include <iostream>
#include <vector>

#define ll long long 

using namespace std;

ll n, m, i, j, act, last;

int main()
{
    cin >> n;
    vector <ll> x(n, 0);
    vector <bool> seen(n, false);
    for (i = 0; i < n; ++i) cin >> x[i];

    ll db = 0;
    i = 0;
    while (db!=n)
    {
        if (act != 0)
        {
            if (last >= i)
            {
                x[i] = (x[i] + 1) % n;
            }
            else 
            {
                j = 1;
                while (j <= act)
                {
                    x[i] = (x[i] + 1) % n;
                    ++j;
                }
            }
            if (!seen[x[i]])
            {
                seen[x[i]] = true;
                db++;
            }
           
        }
        else if (!seen[x[i]])
        {
            seen[x[i]] = true;
            db++;
        }
        if (seen[i]) ++i;
        else
        {
            last = i;
            act++;
            i = 0;
        }
    }
    cout << act;
    return 0;
}