#include <iostream>
#include <fstream>

using namespace std;

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

int a[2000001];

int main()
{
    int n, i, j, nr;
    fin >> n;
    for (i = 2; i * i <= n; i++)
        if (a[i] == 0)
            for (j = i * i; j <= n; j += i)
                a[j] = 1;
    nr = 1;
    for (i = 3; i <= n; i += 2)
        if (a[i] == 0)
            nr++;
    fout << nr;
    return 0;
}