#include <stdio.h>
#include <stdlib.h>
int v[2000000];
int main()
{
    FILE *fin, *fout;
    int n,c,i,nr;
    fin=fopen("ciur.in","r");
    fscanf(fin,"%d",&n);
    fclose(fin);
    nr=0;
    for(i=2;i<=n;i++){
      if(v[i]==0){
        for(c=i*i;c<=n;c=c+i)
          v[c]=1;
        nr++;
        //printf("%d\n",i);
      }
    }
    fout=fopen("ciur.out","w");
    fprintf(fout,"%d",nr);
    fclose(fout);
    return 0;
}