#include <fstream>
#include <iostream>
using namespace std;
  	ifstream f ("ciur.in");
	ofstream o ("ciur.out");
int main() {
	int i,ii,j,x;
    int a[100];
	f>>x;

	for (i=1;i<x;i++){
		if(a[i]!=1) {j++; if(i*i>x){break;} for(ii=i;i<x;ii=ii+i){a[ii]=1;}}
	}

	
	o<<j;
	o.close();
	f.close();
	return 0;   
	
}