#include <bits/stdc++.h>
using namespace std;
#define _11037_ ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
#define endl '\n'
#define inf 2e9
#define MAX 100005
#define MOD 998244353
int N, X, a[MAX];
int BFS(int start)
{
    int vis[MAX] = {0};
    queue<pair<int, int>> que;
    que.push({1, a[0]});
    while (que.size())
    {
        int nowstep = que.front().first, now = que.front().second;
        que.pop();
        if (!vis[(now + 1) % N])
        {
            vis[(now + 1) % N] = 1, que.push({nowstep + 1, (now + 1) % N});
            if ((now + 1) % N == X)
                return nowstep + 1;
        }
        if (!vis[(now + a[now]) % N])
        {
            vis[(now + a[now]) % N], que.push({nowstep + 1, (now + a[now]) % N});
            if ((now + a[now]) % N == X)
                return nowstep + 1;
        }
    }
    return inf;
}
signed main()
{
    _11037_
    cin >> N >> X;
    for (int i = 0; i < N; i++)
        cin >> a[i];
    cout << BFS(0) << endl;
}