#include <iostream> #include <cstdio> #include <queue> #include <algorithm> #include <cmath> #include <cstring> #define inf 2147483647 #define N 2000010 #define mod 1000000007 #define p(a) putchar(a) #define For(i,a,b) for(long long i=a;i<=b;++i) //by war //2019.8.21 using namespace std; long long n,tot[N],num,cnt,ans,temp; long long prime[N],mu[N]; bool vis[N]; void in(long long &x){ long long y=1;char c=getchar();x=0; while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();} while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();} x*=y; } void o(long long x){ if(x<0){p('-');x=-x;} if(x>9)o(x/10); p(x%10+'0'); } void Euler(){ mu[1]=1; For(i,2,2e6){ if(!vis[i]) prime[++cnt]=i,mu[i]=-1; for(long long j=1;j<=cnt&&i*prime[j]<=2e6;j++){ vis[i*prime[j]]=1; if(i%prime[j]==0){ mu[i*prime[j]]=0; break; } mu[i*prime[j]]=-mu[i]; } } } signed main(){ in(n); Euler(); For(i,1,n){ temp=0; for(long long d=i;d<=n;d+=i){ num=n/d; temp+=mu[d/i]*num*(num-1)/2; } ans+=temp*i; } o(ans); return 0; }