#include <cstdio>

using namespace std;

int n,x,nr=0;
char a[2000000];

void ciur()
{
    for (int i=2; i<=n; i++)
    {
        if(a[i]==0)
        {
            for (int j=i+i; j<=n; j=j+i)
                a[j]=1;
            nr++;
        }
    }
}

int main()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf ("%d",&n);
    ciur();
    printf("%d",nr);
    return 0;
}