#include <stdio.h>
char v[2000000];
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    int n,nr=0,i,j;
    fscanf(fin,"%d",&n);
    for(i=0; i<=n; i++)
      v[i]=1;
    for(i=4; i<=n; i=i+2)
      v[i]=0;
    for(i=3; i<=n; i=i+2)
      if(v[i]==1)
        for(j=i*i; j<=n; j=j+i)
          v[j]=0;
    for(i=2; i<=n; i++)
     if(v[i]==1)
       nr++;
    fprintf(fout,"%d",nr);
    return 0;
}