#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool prim[2000005];

int main()
{
    int i,n,k=0,j;
    fin>>n;
    for(i=1;i<=n;i+=2)
        prim[i]=1;
    prim[1]=0;
    prim[2]=1;
    for(i=3;i*i<=n;i=i+2)
    {
        if(prim[i]==1)
            for(j=i*i;j<=n;j=j+2*i)
            {
                prim[j]=0;
            }
    }
    for(i=1;i<=n;i++)
    {
        if(prim[i]==1)
            k++;
    }
    fout<<k;

    return 0;
}