#include <bits/stdc++.h>
#include <fstream>
#define endl '\n'
#define mod 1000000007
#define INF 1000000000
#define INF2 2000000000000000000
//#define ll long long
///#define cin fin
///#define cout fout
using namespace std;
double const EPS = 1e-14;
///ofstream fout("herding.out");
///ifstream fin("herding.in");
const int N = 1e5 + 5;
vector<pair<int,bool>> v[N];
pair<int,bool> dis[N];
int x; 
void bfs(int s) {
    for(int i = 0; i < N; i++) dis[i].first = INF;
    dis[s] = {0,0};
    queue<int> q;
    q.push(s);
    while(!q.empty()) {
        int cur = q.front();
        q.pop();
        for(auto i : v[cur]) {
            //cout << cur << ' ' << i.first  << 'd' << endl;
            if(dis[cur].second == 0 && i.second == 1) continue;
            if((dis[i.first].first > dis[cur].first+1)) {
                dis[i.first].first = dis[cur].first+1;
                dis[i.first].second = 1;
                q.push(i.first);
            }
            else if(dis[x].first == INF) {
                dis[i.first].first = dis[cur].first+1;
                dis[i.first].second = 1;
                q.push(i.first);
            }
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(0);cout.tie(0);cin.tie(0);
    int n; cin >> n >> x; int arr[n];
    for(int i = 0; i < n; i++) {
        int y; cin >> y;
        v[i].push_back({(i+y)%n,0});
        v[i].push_back({(i+1)%n,1});
    }
    bfs(0); cout << dis[x].first << endl;
    //for(int i = 0; i < n; i++) cout << i << ' ' << dis[i].first << ' ' << dis[i].second << endl;
    return 0;
}