#include <fstream>
#include <cmath>
using namespace std;
   bool v[2000001];
    int i,a,j,r;
int main()
{
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
     f>>a;
    v[0]=1;
    v[1]=1;
    for (i=1;i<=int(sqrt(a));i++)
        if (v[i]==0) for (j=2;j<=a/i;j++)
        v[i*j]=1;
    for (i=1;i<=a;i++)
        if (v[i]==0) r++;
        g<<r;
}