#include<stdio.h>
int main()
{
int n,i,j,s;
FILE* f=fopen("ciur.in","r");
FILE* g=fopen("ciur.out","w");
fscanf(f,"%d",&n);
#define nmax n
int a[1000001]={0};
a[0]=1;a[1]=1;
i=2;s=0;
for(i=2;i<=n;i++)
{
  if(a[i]==0)
   { 
     for(j=i+i;j<=n;j+=i)
        a[j]=1;
      s++;
    }
}
fprintf(g,"%d",s);
fclose(f);
fclose(g);
return 0;
}