#include<fstream>
#include<bitset>
#define Nmax 2000099
using namespace std;

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

int n,k,p[Nmax];
bitset <Nmax> b;


int main()
{
    f>>n;
    k=1;
    p[k]=2;
    for(int i=4;i<=n;i+=2)
        b[i]=1;
    for(int i=3;i<=n;i+=2)
        if(b[i]==0)
        {
            ++k;
            p[k]=i;
            for(int j=2*i;j<=n;j+=i) b[j]=1;
        }
    g<<k<<'\n';
    f.close();g.close();
    return 0;
}