#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int n, cnt;
char prim[2000005];

int main()
{
    int i, j;

    fin >> n;
    for (i = 2; i <= n; ++i)
        prim[i] = 1;

    for (i = 2; i <= n; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }

    fout << cnt;
    fout << endl;

    return 0;
}