#include <iostream>
#include  <fstream>
#include    <bitset>
using namespace std;
bitset<2000005>a;
int n;

int main()
{
    int i, j,k;
    ifstream fin("ciur.in");
    ofstream fout ("ciur.out");
    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;
}