悬棺

#include<bits/stdc++.h>
using namespace std;
const int maxn=10000005;
bool p[maxn];
long long v[maxn],prime[maxn],l,r,m,a[maxn],need=0;
void pri(long long n)//线性筛
{
	memset(v,0,sizeof(v));
	 m=0;
	for(int i=2;i<=n;i++)
	{
		if(v[i]==0)
		{need++;
			v[i]=i;
			prime[++m]=i;
		}
		for(int j=1;j<=m;j++)
		{
			if(prime[j]>v[i]||prime[j]>n/i)break;
			v[i*prime[j]]=prime[j];
		}
	}
}
int main(){
cin>>l;
pri(l);
cout<<need;
return 0;
}