/*
 	ciurul lui eratostene
 */
#include <fstream>
#include <iostream>
using namespace std;
int main(){
	int *v , n ,r, i , j;
	ifstream fin("ciur.in"); fin>>n;fin.close();
	v= new int[n+1];
	for(i=0;i<=n;i++)
		v[i]=1;
	r=1,i=2;for(j=2;j*i<=n;j++)	v[i*j] = 0;
	for(i=3;i<=n;i+=2)
		if(v[i]==1)
			for(j=2,r++;j*i<=n;j++)
				v[i*j] = 0;
	ofstream fout("ciur.out"); fout<<r; fout.close();
	return 0;
}