#include<fstream.h>
 ifstream f("ciur.in");
 ofstream g("ciur.out");
    int n2,prim=1,j,n,a[1000002],i;
    int main(){
        f>>n;
        n2=n/2;
        i=3;
        while(i<=n2){
            do{
                i++;
            }while(a[i]);
            for(j=i+i;j<=n;j+=i) a[j]=1;
            prim++;
        }
        g<<prim<<'\n';
        g.close();
        return 0;
    }