#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
const int lim=2e6+3;
bool primes[lim];
int main()
{
    int n,answer=0;
    cin>>n;
    for(int i=2;i<=n;++i)
    if(primes[i]==0)
    {
        answer++;
        for(int j=2*i;j<=n;j+=i)
            primes[j]=1;
    }
    cout<<answer;
    return 0;
}