#define _USE_MATH_DEFINES #include using namespace std; //template #define rep(i,a,b) for(int i=(a);i<(b);i++) #define rrep(i,a,b) for(int i=(a);i>(b);i--) #define ALL(v) (v).begin(),(v).end() typedef long long int ll; const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12; void tostr(ll x,string& res){while(x)res+=('0'+(x%10)),x/=10; reverse(ALL(res)); return;} template inline bool chmax(T& a,T b){ if(a inline bool chmin(T& a,T b){ if(a>b){a=b;return 1;}return 0; } //template end int main(){ int n; scanf("%d",&n); int x=0; rep(i,0,n){ int tmp; scanf("%d",&tmp); if(tmp>0)x=__gcd(x,tmp); } printf(x==0?"-1\n":"%lld\n",1LL*x*x); return 0; }