#include<bits/stdc++.h>
#define Me(x,y) memset(x,y,sizeof x)
using namespace std;
const int N=5e5+5;
int n,k,A[N];
int dis[N];
void Solve(){
	scanf("%d%d",&n,&k);
	for(int i=0;i<n;i++) scanf("%d",&A[i]);
	Me(dis,0x3f);
	dis[0]=0;
	queue<int> q;
	q.push(0);
	int flag=0;
	while(!q.empty()){
		int x=q.front();q.pop();
		if(dis[x]){
			int y=(x+1)%n;
			if(!y&&!flag){
				dis[0]=dis[x]+1;
				q.push(0);
				flag=1;
			}
			else if(dis[y]>dis[x]+1) dis[y]=dis[x]+1,q.push(y);
		}
		int y=(x+A[x])%n;
		if(!y&&!flag){
			dis[0]=dis[x]+1;
			q.push(0);
			flag=1;
		}else{
			if(dis[y]>dis[x]+1) dis[y]=dis[x]+1,q.push(y);
		}
	}
	printf("%d\n",dis[k]);
}
int main(){
	int t=1;
	// scanf("%d",&t);
	while(t--) Solve();
	return 0;
}