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