#include <stdio.h>
#include <math.h>
using namespace std;
int v[2000005],n,nr;
void ciur()
{
    int i,j,lim;
    lim=sqrt(n);
    v[0]=1;
    v[1]=1;
  /*  for(i=4;i<=n;i+=2)
        v[i]=1;
*/
    for(i=3;i<=lim;i+=2)
        if(v[i]==0)
            for(j=i*i;j<=n;j+=2*i)
                v[j]=1;
}
int main()
{
    int i,nr=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    ciur();
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
            nr++;

    printf("%d",nr+1);
    return 0;
}