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

int main() {
        int n, x; cin >> n >> x;
        vector<int> a(n); for (int &i : a) cin >> i;

        vector<bool> seen(n);
        set<int> next = {a[0]};

        for (int _ = 1; _ <= n; _++) {
                set<int> next2;
                for (int i : next) {
                        if (i == x) {
                                cout << _ << '\n';
                                return 0;
                        }
                        seen[i] = true;

                        if (!seen[(i+a[i])%n]) {
                                next2.emplace((i+a[i])%n);
                        } else if (!seen[(i+1) % n]) {
                                next2.emplace((i+1) % n);
                        }
                }
                next = next2;
        }
        assert(0);
}