#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i=0;i<(int)(n);i++)

int main(){
  int n;
  cin>>n;
  vector<int> a(n);
  rep(i,n) cin>>a.at(i);
  vector<int> b(9);
  rep(i,n) b.at(a.at(i))++;
  ll ans=0;
  rep(i,n){
    ll nw=1;
    rep(j,9){
      ans+=nw*b.at(j);
      nw*=a.at(i);
    }
  }
  cout<<ans<<endl;
}