#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int vm=1000001;
bool c[vm];
int main()
{
    int n,i,j,nrprim=0;
    fin>>n;
    for(i=2;i<=n;++i)
        if(!c[i])
        {for(j=i*i;j<=n;j+=i)
                c[j]=true;
        nrprim++;
        }
    fout<<nrprim;
    return 0;
}