#include <stdio.h>

char a[2000005];
int n,nr=0;

int main(){
           int i,j;
           freopen("ciur.in","r",stdin);
           freopen("ciur.out","w",stdout);
           scanf("%d",&n);
           for(i=2;i<=n;i++)
               a[i]=1;
           for(i=2;i<=n;i++)
               if(a[i]==1){
                   nr++;
                   for(j=i+i;j<=n;j+=i)
                       a[j]=0;
               }
           printf("%d\n",nr);
           fclose(stdout);
           return 0;
}