ソースコード
#include <iostream>
#include <fstream>
#include <cassert>
#include <typeinfo>
#include <vector>
#include <stack>
#include <cmath>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <cstdio>
#include <queue>
#include <iomanip>
#include <cctype>
#include <random>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<P,string> pip;
typedef vector<pip> vip;
const int inf=1<<29;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-8;
const ll mod=1e9+7;
const int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};
int f(vi a,vi b,bool& flag){
int A=(a.empty()?inf:a[0]),B=(b.size()<2?inf:b[0]+b[1]);
if(A==inf&&B==inf) flag=0;
return min(A,B);
}
int n;
vvi a(3);
int main(){
cin>>n;
int res=0;
for(int i=0;i<n;i++){
int A;
cin>>A;
res+=A;
a[A%3].push_back(A);
}
sort(a[1].begin(),a[1].end());
sort(a[2].begin(),a[2].end());
bool flag=1;
if(res%3==2) swap(a[1],a[2]);
if(res%3!=0) res-=f(a[1],a[2],flag);
if(res&&flag) cout<<res<<endl;
else cout<<-1<<endl;
}