#include<fstream>
using namespace std;

int n,cnt;
bool prim[2000005];

int main()
{
    int i,j;
    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
        if (prim[i]!=0)
            {cnt++;
             for (j=i+i;j<=n;j=j+i)
                prim[j]=0;
            }
    ofstream fout("ciur.out");
    fout<<cnt<<"\n";
    fout.close();
    return 0;
}