#include<fstream>

using namespace std;

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

int pr[500000];
bool lp[2000000];
int i,j,k,m,u,n;

int main()
{
    cin>>n;
    for (int i=2; i<=n; ++i)
    {
        if (!lp[i])
        {
            pr[++u]=i;
        }
        for (j=1; j<=u && pr[j]*i<=n;  ++j) lp[i*pr[j]]=1;
    }
    int sol=0;
    for (i=2; i<=n; ++i)
        if (!lp[i]) ++sol;
    cout<<sol;
    return 0;
}