#include <stdio.h>
#include <bitset>
using namespace std;
int n,i,nr,j;
bitset <2000001> t;
int main(){
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n); nr=n-1;
for (i=2;i*i<=n;i++)
   if (t[i]==0) {
    for (j=i*i;j<=n;j+=2*i) {
        if (t[j]==0) nr=nr-1; t[j]=1;
   }
}
printf("%d\n",nr);
return 0;
}