#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}, dis[MAX];
    for (int i = 0; i < MAX; i++)
        dis[i] = inf;
    priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> que;
    que.push({0, 0}), dis[0] = 0, vis[0] = 1;
    while (que.size())
    {
        int nowstep = que.top().first, now = que.top().second;
        if (now == X)
            return dis[X];
        que.pop();
        if (vis[(now + a[now] + 1) % N])
            continue;
        vis[(now + a[now] + 1) % N] = 1;
        dis[(now + a[now] + 1) % N] = min(dis[(now + a[now] + 1) % N], nowstep + 1 + 1);
        que.push({dis[(now + a[now] + 1) % N], (now + a[now] + 1) % N});
    }
    return dis[X];
}
signed main()
{
    _11037_
    cin >> N >> X;
    for (int i = 0; i < N; i++)
        cin >> a[i];
    cout << BFS(0) << endl;
}