#include<cstdio>
#define re register int
long long n,ans,f[2000010];
int main(){
    scanf("%lld",&n);
    for(re i=n;i;--i){
        f[i]=n/i*(n/i);
        for(re j=i<<1;j<=n;j+=i)f[i]-=f[j];
        ans+=f[i]*i;
    }
    printf("%lld",(ans-n*(n+1)/2)/2);
return 0;
}