#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);
          
    for(i=2;i<=n;i++)
    a[i]=1;
    for(j=2;j<=n;j++)
    if (a[j]==1){
                 k++;
                 for(j=i*i;j<=n;j+=i){
                                      a[j]=0;
                                      }
                                      fprintf(g,"%d",k);
                                      return 0;
}