#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, nr = 0;
    fin >> n;
    bool prim[n + 1];
    for (int i = 2; i <= n; i++)
        prim[i] = 1;
    for (int i = 2; i <= sqrt(n); i++)
        if (prim[i])
        for (int j = i + i; j <= n; j += i)
        prim[j] = 0;
    for (int i = 2; i <= n; i++)
        if (prim[i])
        nr++;
    fout << nr;
    return 0;
}