#include <fstream>

using namespace std;

int main()
{
    int c=1,n,i,j;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    int v[n]={20000};
    for(i=3;i<=n;i+=2)
    {
        if(v[i]==0)
            for(j=i+2*i;j<=n;j=j+2*i)
            {
                v[j]=1;
            }
    }
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
            c++;
    fout<<c;
    return 0;
}