#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<queue>
#define N 100010
using namespace std;

int n,x,a[N],step[N];
struct node{
	int i,t,step;
};
queue<node> q;

void bfs(){
	node tmp={0,0,0};
	step[a[0]+0]=1;
	q.push(tmp);
	while(!q.empty()){
		int i=q.front().i,t=q.front().t,s=q.front().step;
		if((i+a[i]+t)%n!=0&&step[(i+a[i]+t)%n]==0){
			node Tmp={(i+a[i]+t)%n,0,s+1};
			q.push(Tmp);
			step[(i+a[i]+t)%n]=s+1;
		}
		if(t<n-1){
			node Tmp={i,t+1,s+1};
			q.push(Tmp);
		}
		q.pop();
	}
}

int main(){
	cin>>n>>x;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	bfs();
	cout<<step[x]<<"\n";
	return 0;

}