#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int i,j,v[2000000/2+1],n,nr;
int main()
{
    fin>>n;
    nr=1;
    for(i=3;(i<< 1)+1<=n;i+=2)
    {
        if(v[i]==0)
        {nr++;
        for(j=i+i+i;(j << 1) + 1<=n;j+=(i << 1)+1)
            v[j]=1;}
    }
    fout<<nr;
    return 0;
}