#include <cstdio>

int n,numar;
int a[2000010];

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