#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
    int n,i,gigi,j;
    in>>n;
    gigi=0;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
        gigi++;
        for(j=i*2;j<=n;j=j+i)
        {
            v[j]=1;
        }
        }

    }
    out<<gigi;
    return 0;
}