#include<stdio.h>
FILE *in=fopen("ciur.in","r");   
FILE *out=fopen("ciur.out","w");   
int main()   
{   
 char v[2000001];   
  
 long int i,n,nr=1,j;   
 fscanf(in,"%ld",&n);   
 for(i=0;i<=n;i++) v[i]=0;   
 for(i=3;i<=n;i=i+2)   
 {   
    if(v[i]==0)   
    {   
     nr++;   
     for(j=i+i+i;j<=n;j=j+2*i)   
            v[j]=1;   
    }   
 }   
 fprintf(out,"%ld",nr);   
 return 0;   
}