#include <fstream>

using namespace std;

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

bool ciur[2000005];

int main()
{
    int n, nr = 0, i, j;
    f >> n;
    for (i = 2; i <= n; i++)
        if (ciur[i] == 0)
        {
            nr++;
            for (j = i+i; j <= n; j += i)
                ciur[j] = 1;
        }
    g << nr;
    return 0;
}