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

const int N = 24;
int n, a[N], b[N], T;

int main()
{
    while (cin >> n, n)
    {
        for (int i = 0; i < n; ++ i) cin >> a[i];
        for (int i = 0; i < n-1; ++ i) b[i] = a[i+1] - a[i];

        if (n == 1) 
        {
            cout << 0 << endl;
            continue;
        }

        for (int len = 1; len < n; ++ len) //枚举周期的长度
        {
            bool f = 1;//第一个周期后面的数字和len位置数比较
            for (int i = len; i < n-1; ++ i) 
                if (b[i] != b[i%len])
                {
                    f = 0;
                    break;
                }
            if (f)
            {
                cout << len << endl;
                break;
            }
        }
    }
    return 0;
}