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

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