#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,i,d,prime=1,a,prim;
    scanf("%d",&n);
    for(i=3;i<=n;i+=2)
    {
        a=sqrt(i);
        prim=0;
        for(d=3;d<=a;d+=2)
            if(i%d==0)
            {
                prim=1;
                break;
            }
    if(prim==0)
        prime++;
    }
    printf("%d",prime);
}