#include <iostream>
#include <fstream>
#include <iostream>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
using namespace std;
const int M=2e6+1;
bool locuri[M];
int main()
{
    int n; int s=0;
    fin>>n;
    for(int i=2;i<=n;i++){
        if(!locuri[i]){
    for(int j=i+i;j<=n;j+=i){
        locuri[j]=1;}
        s++;}}
        fout<<s;
        return 0;}