#include <stdio.h>
#include <bitset>
using namespace std;
long n,i,j,q;
bitset <2000001>prim;
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    q=1;
    for (i=3;i<=n;i+=2)
        if (!prim[i]){
            q++;
            for (j=3*i;j<=n;j+=2*i)
                prim[j]=1;
        }
    printf("%ld\n",q);
return 0;
}