#include <fstream>

using namespace std;

char v[2000001];

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

int main()
{
    int n,i;
    in>>n;
    int cnt=0;
    for (i=2;i<=n;i++)
        if (v[i]==0)
           {
            for(unsigned long long j=i*i;j<=n;j+=i)
              v[j]=1;
            cnt++;
           }
    out<<cnt;
    return 0;
}