#include<stdio.h>
#include<math.h>
int a[30000005];
typedef long long ll;
int main()
{
    ll n;
    scanf("%lld",&n);
    ll x,i,j;
    ll k=sqrt(n);
    ll sum=0;
    for(i=2; i<=n; i++)
    {
        if(!a[i])
        {
            sum+=i;
            for(j=i*i; j<=n; j+=i)
            {
                if(!a[j])
                a[j]=1,sum+=i;
            }
        }
    }
    printf("%lld\n",sum);

    return 0;
}