/*
Author: haze
2023/12/23
13:34
*/

#include <bits/stdc++.h>

#define irep(i, l, r) for(int (i) = (l); (i) <= (r); ++(i))
#define drep(i, r, l) for(int (i) = (r); (i) >= (l); --(i))
#define ll long long
#define LL __int128
using namespace std;

inline ll read() {
    char ch = getchar();
    ll s = 0;
    bool w = 0;
    while (!isdigit(ch)) {
        if (ch == '-')w = 1;
        ch = getchar();
    }
    while (isdigit(ch))s = (s << 3) + (s << 1) + (ch ^ 48), ch = getchar();
    return w ? -s : s;
}

inline char rc() {
    char ch = getchar();
    while (1) {
        if (ch >= '!' && ch <= '~')return ch;
        ch = getchar();
    }
}

template<class T1, class T2>
T1 min(T1 AA, T2 BB) { return AA > BB ? BB : AA; }

template<class T1, class T2>
T1 max(T1 AA, T2 BB) { return AA < BB ? BB : AA; }

const int itinf = 1e9;
const ll llinf = 4e18;
const int mod = 1000000007;
const int N = 500009;

int main() {
    int n = read(), t = read();
    vector<int>nxt(n), fl(n);
    irep(i, 0, n - 1){
        nxt[i] = (i + read()) % n;
        fl[nxt[i]] = 1;
    }
    vector<int>dis(n, itinf);
    dis[nxt[0]] = 1;
    queue<int>q;
    q.push(nxt[0]);
    while(q.size()){
        int x = q.front();
        q.pop();
        if(dis[nxt[x]] > dis[x] + 1){
            dis[nxt[x]] = dis[x] + 1;
            q.push(nxt[x]);
        }
        if(dis[(x + 1) % n] > dis[x] + 1){
            dis[(x + 1) % n] = dis[x] + 1;
            q.push(x + 1);
        }
    }

    cout << dis[t];
    return 0;
}