#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool w[2000005];
int n, i, j, nr;

int main()
{
    f >> n;

    w[1] = w[0] = true;

    for(i = 2; i <= n; ++ i)
        if(w[i] == false)
        {
            nr ++;
            for(j = i + i; j <= n; j += i)
                w[j] = true;
        }

    g << nr << "\n";

    return 0;
}