#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int v[2000010],i,j,n,c;

int main()
{
    fin>>n;
    v[1]=1;
    for (i=2;i<=n/2;i++)
        if (v[i]==0)
            for (j=2*i;j<=n;j+=i)
                v[j]=1;
    for (i=1;i<=n;i++)
        if (v[i]==0)
            c++;
    fout<<c;
    return 0;
}