#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N,v[2000000],j,nrp,i;

int main()
{
    fin>>N;
    for(i=2;i<=N;++i)v[i]=1;
    for(i=2;i<=N;++i)
    {
        if(v[i]==1)
        {
            ++nrp;
            for(j=i+i;j<=N;j+=i)v[j]=0;
        }
    }
    fout<<nrp;

    return 0;
}