#include <fstream>

using namespace std;
long long v[2000000];
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n, contor=0;
    in >> n;
    for(int i=2;i<=n;i++)
        if(!v[i])
        {
            contor++;
            for(int j=i*i;j<=n;j+=i)
            v[j]=true;
        }
    out << contor;
    return 0;
}