#include <stdio.h>
#include <stdlib.h>
char v[200000000];
int main()
{   FILE*fi,*fout;
    int con,n,i,j;
    fi=fopen("ciur.in" ,"r");
    fout=fopen("ciur.out" ,"w");
    fscanf(fi,"%d" ,&n);
    for(i=2;i*i<=n;i++)
     if(v[i]==0)
       for(j=i*i;j<=n;j=j+i)
         v[j]=1;
    con=0;
    for(i=2;i<=n;i++)
         if(v[i]==0)
            con++;
    fprintf(fout,"%d" ,con);
    fclose(fi);
    fclose(fout);
    return 0;
}