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