#include <fstream>

using namespace std;
int N,i,j,nr;
bool p[2000002];
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int main()
{
    f>>N;
    for (i=2;i<=N;i++) p[i]=true;
    for (i=2;i*i<=N;i++) {
        if (p[i])
            for (j=2*i;j<=N;j+=i) p[j]=false;
    }
    for (i=2;i<=N;i++)
        if (p[i]) nr++;
    g<<nr;
    return 0;
}