#include <iostream>

using namespace std;

bool ciur[2000001];

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

int main()
{
    int d,i,n,x=0;
    in>>n;
    for (i=2;i<=n;i++)
    {
        if (ciur[d]==0)
        {
            for (i=d*2;i<=n;i+=d)
            {
                ciur[i]=1;
            }
        }
    }
    for (i=2;i<=n;i++)
    {
        if (ciur[i]==0)
            x++;
    }
    out<<x;
    return 0;
}