#include <iostream>
#include <fstream>
#include <cstring>
#include <string>
#include <climits>
#include <algorithm>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout("ciur.out");

#define MAX 801

int n,i,j;
bool a[2000001];

int main()
{
    fin>>n;
    int k=1;
    for(i=3;i<=n;i+=2)
    {
        if(!a[i])
        {
            k++;
            for(j=2;i*j<=n;j++)
            {
                a[i*j]=1;
            }
        }
    }
    fout<<k;

    return 0;
}