#include<fstream>
#include<bitset>
using namespace std;
bitset<2000001> a;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int i,j,k,n;
    fin>>n;
    for(i=4;i<=n;i=i+2)
        a[i]=1;
    for(i=3;i*i<=n;i=i+2)
        if(a[i]==0)
        for(j=i*i;j<=n;j=j+2*i)a[j]=1;
    k=1;
    for(i=3;i<=n;i=i+2)
        if(a[i]==0)k++;
    fout<<k<<"\n";
    fin.close();
    fout.close();
    return 0;
}