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

int main() {
    cin.tie(0)->sync_with_stdio(0);

    int n, k;
    cin >> n >> k;
    vector<int> a(n);
    for (auto &e: a)
        cin >> e;

    vector<set<int>> g(n);
    for (int i = 0; i < n; i++) {
        g[i].emplace((i+1)%n);
        g[i].emplace((i+a[i])%n);
    }

    queue<pair<int, int>> q;
    q.push({0, 0});
    while (q.size()) {
        auto [u, c] = q.front(); q.pop();
        for (auto v: g[u]) {
            if (c == 0 && v == 1) continue;
            if (v == k) {
                cout << c+1 << endl;
                return 0;
            }
            q.push({v, c+1});
        }
    }

    return 0;
}