// #pragma GCC optimize(3)
#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
using u64 = unsigned long long;
using ld = long double;
using i128 = __int128_t;
using u128 = __uint128_t;
#define int long long
#define mem(a, b) memset((a), (b), sizeof(a))
#define all(a) (a).begin(), (a).end()
#define lowbit(x) (-x) & x
#define debug cout<<"$"
#define ls u << 1
#define rs u << 1 | 1
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
using pi = pair<int,int>;
using p3 = tuple<int,int,int>;
mt19937 rnd(time(0));
const int MOD = 1e9+7;
const ld eps = 1;
int qmi(int m, int k){int res = 1, t = m;while (k){if (k & 1) res = (res * t) % MOD;t = t * t % MOD;k >>= 1;}return res;}
const int N = 2e6 + 7;
const int inf = 1e18 + 7;
void solve()
{
    int n,x;
    cin>>n>>x;
    vector<int> ans(n,inf);
    // vector<int> len(n);
    vector<int> a(n);
    for(int i=0;i<n;i++)    cin>>a[i];
    if(x==0)    return cout<<"0\n",void();
    priority_queue<p3,vector<p3>,greater<p3>> q1;
    q1.push({1,0,1});
    while(1)
    {
        auto [now,st,len] = q1.top();
        q1.pop();
        if(st==x)   return cout<<now-len<<"\n",void();
        q1.push({now+1,st,len+1});
        q1.push({now+2,(st+len+a[st])%n,1});
    }
}   
signed main()
{
    // freopen("test.in","r",stdin);
    // freopen("test.in","w",stdout);
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int T = 1;
    // cin>>T;
    while (T--)
        solve();
}
/*
1 2 7
3 5
4 6


*/