//Cirul lui Erastotene
#include <cstdio>
char p[2000001];
int n,i,j;
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for (i=2;i<=n;i++) p[i]=1;
    for (i=2;i<=n;i++)
     if (p[i]) 
      for (j=2;i*j<=n;j++) p[i*j]=0;
    j=0;
    for (i=2;i<=n;i++) if (p[i]) j++;
    printf("%d",j);
    fclose(stdout);
    return 0;
}