#include <fstream>
using namespace std;
int n,i,k,p=0,x;
bool ok[2000001];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for (i=2;i<=n;i++)ok[i]=true;
    for (i=2;i<=n;i++)
    {
        if (ok[i])
        {
            p++;
            for (k=2*i;k<=n;k+=i)
            ok[k]=false;
        }
    }
    g << p;
    return 0;
}