#include <fstream>
using namespace std;
ifstream cin ("ciur.in");
ofstream cout("ciur.out");
bool prim[2000005];
int main(){
    int n,ans=0,i,j;
    cin>>n;
    for(i=2;i<=n;++i){
       if(prim[i]==0){
           ++ans;
           for(j=2*i;j<=n;j+=i)
               prim[j]=1;
       }
    }
    cout<<ans;
    return 0;
}