#include <iostream>
#include <fstream>

using namespace std;
bool a[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,nr=1;
    scanf("%d",&n);
        for(int i=3;i<=n;i+=2)
           if(!a[i])
           {
            nr++;
            for(int j=i*i;j<=n;j+=i)
              a[j]=true;
           }


      printf("%d",nr);
    return 0;
}