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