#include <fstream>

using namespace std;

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

const int N=2000000+5;
int n,ans=1;
bool co[N];

int main()
{
    fin>>n;
    for(int i=4;i<=n;i+=2)
    {
        co[i]=1;
    }
    for(int i=3;i*i<=n;i+=2)
    {
        if(co[i]==0)
        {
            for(int j=i*i;j<=n;j+=2*i)
            {
                co[j]=1;
            }
        }
    }
    for(int i=3;i<=n;i+=2)
    {
        if(co[i]==0)
        {
            ans++;
        }
    }
    fout<<ans<<"\n";
    return 0;
}