#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = 998244353;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll modpow(ll x, ll p) { ll result = 1, now = 1, pm = x; while (now<=p) { if (p&now) { result = result * pm % MOD; } now*=2; pm = pm*pm % MOD; } return result; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }


int main() {
  ll N; cin >> N;
  vector<ll> A(N); rep(i,N) { cin >> A[i]; A[i] *= -1; }
  sort(all(A));
  ll mdiff = 0; rep(i,N-1) mdiff = max(mdiff, A[i+1]-A[i]);

  ll MA = 2501;
  ll count[MA] = {};
  repr(d,mdiff,MA) {
    ll dp[N] = {}; dp[1] = 2;
    repr(i,2,N) {
      ll np = lower_bound(all(A),A[i]-d) - A.begin();
      if (i>np) dp[i] = dp[i-1] + (dp[i-1]-dp[np]);
      else dp[i] = dp[i-1];
    }
    // debug(dp, dp+N);
    count[d] = dp[N-1];
  }
  // debug(count, count+MA);

  ll result = 0;
  repr(i,1,MA) result += (count[i]-count[i-1]) * i;
  cout << result << endl;
  return 0;
}