#include <stdio.h>
#include <math.h>
#include <bitset>

using namespace std; 

bitset<2000100> a;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    int n,ret=0,lim;
    
    scanf("%d",&n);
    if (n>=2) ++ret;
    lim = (int)sqrt(n);
        
    for (int i=3;i<=n;i+=2) if(a[i/2] == 0)
    {
        ++ret;
        if (i<=lim) for (int j=i*i;j<=n;j+=2*i) a[j/2] = 1;        
    }
    
    printf("%d\n",ret);
        
    return 0;    
}