# include <fstream>
# include <bitset>
# define DIM  2000010
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,nr,i,j;
bitset <DIM> f;
int main () {
    fin>>n;
    for(i=2;i<=n;i++){
        if(f[i]==0){
            nr++;
            for(j=2*i;j<=n;j+=i)
                f[j]=1;
        }
    }
    fout<<nr<<"\n";
    return 0;
}