#include <fstream>
using namespace std;

int N, nr;
char ciur[2000005];

int main(void)
{
    int i, j;
    ifstream f ("ciur.in");   
    ofstream g ("ciur.out");
    
    f>>N;
    for (i = 2; i <= N; ++i)
        ciur[i] = 1;
    for (i = 2; i <= N; ++i)
        if (ciur[i])
        {
            ++nr;
            for (j = i+i; j <= N; j += i)
                ciur[j] = 0;
        }

    g<<nr<<"\n";

    return 0;
}