#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int fr[2000000],n;

int main()
{
    fin>>n;int k=0;
    for(int i=2;i<=n;++i)
        if(fr[i]==0){k++;
                    for(int j=i*i;j<=n;j=j+i)
                         fr[j]=1;

                    }
    fout<<k;
    return 0;
}