#include<cstdio>
char v[2000001]={0};long i,k,j,n;
int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%ld",&n);
for(i=2;i<=n;i++)
if(v[i]==0)
{
  k++;
   for(j=2;j<=n/i;j++)
  v[i*j]=1;
}
printf("%ld",k);
return 0;}