#include <cstdio>
bool v[2000023];
int n;
int main()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf("%d",&n);
    int ct=1;
    v[1]=1;
    for(int i=4;i<=n;i+=2) v[i]=1;
    for(int i=3;i<=n;i+=2)
    {
        if(v[i]==0)
        {
                ++ct;
                if(i*i<0||i*i>n) continue;
                for(int j=i*i;j<=n;j+=i)
                {
                    v[j]=1;
                }
        }
    }
    printf("%d\n",ct);
}