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