#include <fstream>
#include <bitset>
using namespace std;
bitset <2000005> ciur;
int main(){
	int n, i, j, ras;
	ifstream fin( "ciur.in" );
	ofstream fout( "ciur.out" );
	fin >> n;
	for( i = 2; i * i <= n; i++ ){
		if( ciur[i] == 0 ){
			for( j = i * i; j <= n; j += i ){
				ciur[j] = 1;
			}
		}
	}
	ras = 0;
	for( i = 2; i <= n; i++ ){
		if( ciur[i] == 0 ){
			ras++;
		}
	}
	fout << ras;
	return 0;
}