#include <fstream>
#include <algorithm>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];
int main()
{
    int n,i,j,cnt=0;
    in>>n;
    for (i=3; i<=n; i+=2)
    {
        if (v[i]==0)
        {
            for (j=i*2; j<=n; j+=i)
                v[j]=1;
        }
        cnt++;
    }

    out<<cnt;



    return 0;

}