#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;

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

bool c[2000005];
int main()
{
    int n,contor,aux;
    fin>>n;
    contor=0;
    for (int i=2;i<=sqrt(n);i++)
    {
        if (c[i]==0)
            for (int j=i+i;j<=n;j=j+i)
                c[j]=1;
    }
    for (int i=2;i<=n;i++)
        if (c[i]==0)
            contor++;
    fout<<contor;
    fin.close();
    fout.close();
    return 0;
}