#include <bits/stdc++.h>
 
#define x first
#define y second
#define el '\n'
#define debug(x) cerr << #x << ": " << x << endl
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int N = 3e5 + 10, INF = 0x3f3f3f3f, mod = 998244353;
 
int main() {
    ios::sync_with_stdio(0); cin.tie(0);
    int n, x; cin >> n >> x;
    vector<vector<int>> G(n);
    for (int i = 1; i < n - 1; ++i) G[i].emplace_back(i + 1);
    G[n - 1].emplace_back(0);
    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
        G[i].emplace_back((i + a[i]) % n);
    }
    queue<int> Q;
    vector<int> dis(n, INF);

        Q.push(0);
        dis[0] = 0;

    while (Q.size()) {
        int u = Q.front(); Q.pop();
        for (int v: G[u]) {
            if (dis[v] == INF) {
                dis[v] = dis[u] + 1;
                Q.push(v);
            }
        }
    }
    cout << dis[x] << el;
}