#include <fstream>

using namespace std;

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

bool c[200000001];

int main()
{
    int n, i, j, nr = 0;
    in >> n;
    for (i =  2; i*i <= n; i++)
        if (!c[i])
            for (j = i*i; j <= n; j+=i)
                c[j] = true;


    for (i = 2; i <= n; i++)
        if (!c[i])
            nr++;
    out << nr;


    return 0;
}