#include<stdio.h>
int main()
{ int i,n,k,j;
 char a[200000];
FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
fscanf(f,"%d", &n);
k=1;
                 for (i=2;i<=n;i++)
      if (a[i]==1)
        {
         k++;
         for (j=i*i;j<=n;j=j+i)
            a[j]=1;
         }
         fprintf(g,"%d", k);
         fclose(f);
         fclose(g);
         }