#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;
}