#include <fstream>
#include <bitset>
using namespace std;
bitset <2000005>p;

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

int n,k,i,j;

int main()
{

    f>>n;
    p[1]=1;
    k=1;
    for(i=3;i<=n;i=i+2)
    {
        if(p[i]==0)
        {
            ++k;
            for(j=3;j*i<=n;j=j+2) p[i*j]=1;
        }
    }

    g<<k;

    return 0;
}