#include <iostream>
#include <cstdio>

using namespace std;

bool viz[20000004];
unsigned long int k;

int main(){
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	unsigned long int n;
	cin>>n;
	for(unsigned long int i=2;i<=n;i++)if(!viz[i]){
		unsigned long int temp=i*i;
		if(temp>n)break;
		else for(unsigned long int j=i;j<=n;j++)if(j*i>n)break;else viz[j*i]=1;
	}
	for(unsigned long int i=2;i<=n;i++)if(!viz[i])k++;
	cout<<k;
}