#include <iostream>
#include <fstream>

using namespace std;

char ciur[2000005];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n, d, i, nrp = 0;
    in >> n;
    for(d = 2; d * d <= n; d++)
    {
        if(ciur[d] == 0)
        {
            for(i = d * d; i <= n; i = i + d)
                ciur[i] = 1;
        }
    }
    for(i = 2; i <= n; i++)
    {
        if(ciur[i] == 0)
            nrp++;
    }
    out << nrp;
    in.close();
    out.close();
    return 0;
}