#include<cstdio>
using namespace std;
FILE *fin,*fout;
int cnt;
int i,j;
bool v[2000000];
int main(){
    fin = freopen("ciur.in","r",stdin);
    fout = freopen("ciur.out","w",stdout);
    cnt=0;v[0]=1;v[1]=1;

    for(i=2;2<2000000;i++){
        if(v[i]==0){
          cnt++;
          j=i*i;
          while(j<2000000){
             v[j]=1;
             j=j*2;
          }
        }
    }
    printf("%d",cnt);
    fclose(fin);
    fclose(fout);
    return 0;
}