#include<stdio.h> 
FILE *f,*g; 
int n,i,j,c; 
char v[2000000]; 
int main() { 
    f=fopen("ciur.in","r"); 
    fscanf(f,"%d",&n); 
    fclose(f); 
    j = 2; 
    while(j<=n) 
    { 
        if( v [ j ] != '1')  
         { 
          c++; 
          for(i = j;i <= n;i += j) 
          v [ i ] = '1'; 
         } 
        j++; 
        } 
g=fopen("ciur.out","w"); 
fprintf(g,"%d\n",c); 
fclose(g); 
return 0;
}