#include<bits/stdc++.h>

using namespace std;

#define il inline

#define fi first

#define sc second

#define gc getchar()

#define mp make_pair

#define int long long

#define P pair<int,int>

#define ri register int

#define rc register char

#define rb register bool

#define rp(i,x,y) for(ri i=x;i<=y;++i)

#define my(i,x,y) for(ri i=x;i>=y;--i)

#define e(i,x) for(ri i=head[x];i;i=edge[i].nxt)

const int N=+;

int n,phi[N],sum[N],pr[N],pr_cnt,as;

bool is_pr[N];

il int read()

{

    rc ch=gc;ri x=;rb y=;

    while(ch!='-' && (ch>'' || ch<''))ch=gc;

    if(ch=='-')ch=gc,y=;

    while(ch>='' && ch<='')x=(x<<)+(x<<)+(ch^''),ch=gc;

    return y?x:-x;

}

il void pre()

{

    phi[]=;

    rp(i,,N-)

    {

        if(!is_pr[i])pr[++pr_cnt]=i,phi[i]=i-;;sum[i]=sum[i-]+phi[i];

        rp(j,,pr_cnt)

        {

            if(pr[j]*i>N-)break;;is_pr[pr[j]*i]=;

            if(!(i%pr[j])){phi[i*pr[j]]=phi[i]*pr[j];break;}

            phi[i*pr[j]]=phi[i]*phi[pr[j]];

        }

    }

}

signed main()

{

    //freopen("1390.in","r",stdin);freopen("1390.out","w",stdout);

    pre();n=read();rp(i,,n/)as+=i*sum[n/i];

    printf("%lld\n",as);

    return ;

}