#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

bool x[2000005];

int main()
{
    long long k, n=0;
    in >> k;
    for (long long i=2; i<=k;i++){
        if (!x[i]){
            n++;
            for (long long j = i*i; j<=k; j+=i){
                x[j]=true;
            }
        }
    }
    out<< n;
}