#include<stdio.h>
#include<string.h>
char prim[2000001];
long n,i,j,nr;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    memset(prim,'0',n);
    scanf("%d",&n);
    nr=1;
    if (n==2)
       printf("%d\n",1);
    else
    {
    for (i=3;i<=n;i+=2)
    {        
             if (!prim[i])
             {
                   nr++;
                   for(j=i+i;j<=n;j+=i)
                       prim[j]=1;
             }   
    }
    printf("%d\n",nr);
    }
    return 0;
}