#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char v[250000];
int i,n,j,prime=1;
int main()
{
    fin>>n;
    for(i=3;i<=n;i+=2)
        if(!( v[i/16]& 1<<((i+1)%16/2) ))
        {//cout<<i<<" ";
            prime++;
            for(j=3*i;j<=n;j+=2*i)
                v[j/16]=v[j/16]| 1<<((j+1)%16/2);
        }
    fout<<prime;
return 0;
}