#include <fstream>
#define NMAX 2000005

using namespace std;

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

bool ciur[NMAX];

int main()
{
    int n, i, j, cnt = 0;
    in >> n;

    ciur[0] = 1;
    ciur[1] = 1;
    for (i = 2; i * i < NMAX; ++i)
    {
        if (!ciur[i])
        {
            for (j = i * i; j < NMAX; j = j + i)
                ciur[j] = 1;
        }
    }

    for (i = 1; i <= n; ++i)
    {
        if (ciur[i] == 0)
            ++cnt;
    }

    out << cnt;
    return 0;
}