#include <fstream>
#include <bitset>

using namespace std;
bitset<2000001>a;
int main()
{
   int n,nr=0;
   long long i,j;
   ifstream fin("ciur.in");
   ofstream fout("ciur.out");
   fin>>n;
   for(i=4;i<=n;i+=2)
    a[i]=1;
    for(i=3;i*i<=n;i+=2)
        if(a[i]==0)
            for(j=i*i;j<=n;j+=2*i)
                a[j]=1;
    for(i=2;i<=n;i++)
        if(a[i]==0) nr++;
    fout<<nr<<"\n";
    fin.close();
    fout.close();
    return 0;
}