#include<fstream>
using namespace std;
short v[2000000];
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int c,n,i,j;
    fin>>n;
    c=0;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            c++;
            for(j=i+i;j<=n;j=j+i)
            {
                v[j]=1;
            }
        }
    }
    fout<<c;
    fin.close();
    fout.close();
    return 0;
}