#include<stdio.h>
#define input "ciur.in"
#define output "ciur.out"
char a[2000001];
int main()
{
    freopen(input,"r",stdin);
    freopen(output,"w",stdout);
    int n,i,j,nr=0;
    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;j<=n;j+=i)  
                                   a[j]=0;  
                      }  
                                 }  
                                 printf("%d",nr);  
return 0;  
}