#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
char ciur[2000005];
int n, nr=0;

void facere (){
    for (int i=2; i<=n; i++)
    {
        if (ciur[i]==0)
        {
            for (int j=i*2; j<=n; j+=i)
                ciur[j]=1;
            nr++;
        }
    }
}

int main()
{
    f >> n;
    facere();
    g << nr;
    return 0;
}