#include <fstream>

using namespace std;
bool  prim[2000001];
int main()
{
    int n,i,cnt=0,j;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i=2;i*i<=n;i++)
        if (prim[i]==false)
            for (j=i*i;j<=n;j=j+i)
                prim[j]=true;
    for (i=2;i<=n;i++)
        if (prim[i]==false)
            cnt++;
    g<<cnt;
    return 0;

}