#include <cmath>
#include <fstream>
using namespace std;

bool a[2000000];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int nr=0,n,i,j;
    f>>n;
    if(n>=2)
    {nr=1;
    a[2]=1;
    }
    for(i=3;i<=n;i=i+2)
    a[i]=1;
    for(i=3;i<=sqrt(n);i=i+2)
    for(j=i;j<=n/i;j++)
    a[i*j]=0;
    for(i=3;i<=n;i=i+2)
    if(a[i])
    nr++;
    g<<nr;
    return 0;
}