#include<bits/stdc++.h>
#define fo(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
#define rep(i,l,r) for(ll i(l),i##end(r);i<=i##end;++i)
#define per(i,r,l) for(ll i(r),i##end(l);i>=i##end;--i)
#define dbg(x) cerr<<#x<<" "<<x<<'\n';
#define ll long long
#define gc getchar
#define pc putchar
using namespace std;
namespace WrongIO
{
	#define Ts template<typename Ty,typename... Ar>
	#define Tp template<typename Ty>
	Tp Ty wmax(Ty a,Ty b){return a>=b? a:b;}
	Tp Ty wmin(Ty a,Ty b){return a<=b? a:b;}
	Tp void read(Ty &x){x=0;Ty opt=1;char c=gc();while(!isdigit(c)&&c!='-')c=gc();if(c=='-')opt=-1,c=gc();while(isdigit(c))x=(x<<3)+(x<<1),x+=c-'0',c=gc();x*=opt;return;}
	Tp void write(Ty x){short OI_USE[150],OI_top=0;if(x<=0) if(x==0)pc('0');else pc('-'),x*=-1;while(x)OI_USE[++OI_top]=x%10,x/=10;while(OI_top--)pc(OI_USE[OI_top+1]+'0');return;}
    void writec(char c[]){int len=strlen(c);for(int i=0;i<len;i++)pc(c[i]);}
    void writes(string s){int len=s.length();for(int i=0;i<len;i++)pc(s[i]);}
    void readc(char &c,int l,int r){c=gc(); while(c!=EOF&&(c<l||c>r)) c=gc();}
    void readc(char &c,char val){c=gc();while(c!=EOF&&c!=val) c=gc();}
    void readc(char val){char c;c=gc();while(c!=EOF&&c!=val) c=gc();}
    void readls(string &s){char c=gc();while(c!='\n') s.push_back(c),c=gc();}
    Ts void read(Ty &x,Ar &...y) {read(x),read(y...);}
    Tp void writeln(Ty x) {write(x),pc('\n');}
    Tp void writesp(Ty x) {write(x),pc(' ');} 
    #undef Ts
	#undef Tp
} using namespace WrongIO;
ll val[200050],a[200050],n,ed;
queue<ll> q;
struct awa{
	ll ps,id;
};
bool cmp(awa a,awa b)
{
	return a.ps>b.ps;
}
awa e[200050];
int main()
{
	read(n,ed); ed++;
	rep(i,1,n)
	{
		val[i]=1e9;
		read(a[i]);
		if(i<=ed)
		e[i]=awa{i+a[i],i};
	}
	n=ed;
	sort(e+1,e+n+1,cmp);
	ll minx=1e9,idq=n;
	rep(i,1,n)
	{
		if(e[i].ps>n) continue;
		while(idq>=e[i].ps) ++minx,minx=min(minx,val[idq]),idq--;
		val[e[i].id]=1+min(minx+1,n-e[i].ps);
	}
	write(val[1]);
}