#include <stdio.h>
#include <stdlib.h>
#include <math.h>

char r[8] = {0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80};

int main()
{
       int n, i, j, N, nr = 0;
       char a[2000001];
       FILE *in=fopen("ciur.in","r");
       FILE *out=fopen("ciur.out","w");    
       fscanf(in,"%d",&N);

       memset(a, 0xff, 250001);
       n = sqrt(N) + 1;
       for (i = 2; i <= n; i++)
       {
           if (a[i]) {    
              for (j = i*i; j <= N; j += i)
                  a[j] = 0;
           }                                    
       }
       for (i = 2; i <= N; i++)
           if (a[i])
               nr++;
 
       fprintf(out,"%d",nr);
       fclose(in);
       fclose(out);
       return 0;
}