#include <fstream>

using namespace std;

int n,v[2000110];

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

}