using namespace std;

#include <iostream>
#include <fstream>

const int N=2000005;
bool c[N];

int main(){
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	int nr=0,i,n,j;
	f>>n;
	c[0]=c[1]=true;
	for(i=2;i*i<=n;++i)
		if(!c[i]){
			for(j=i*i;j<=n;j+=i)
				c[j]=true;
		}
	for(i=2;i<=n;++i)
		if(!c[i])
			++nr;
	g<<nr<<endl;
	return 0;
}