#include <iostream>
#include <vector>
#include <string>
#include<fstream>
#include<bitset>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000001> p;
int nr=1;
void ciur(int n){
    int i,j;
    for(i = 4 ;i <= n ;i = i + 2)
    p[i] = 1;
    for(i=3;i <= n;i = i + 2)
    {
        if(p[i] == 0){
            nr++;
            for(j=3 * i; j <= n; j=j +2*i)
            p[j] = 1;
        }
    }
}

int main()
{
   int n;
   fin>>n;
   ciur(n);
   fout<<nr;
}