#include "bits/stdc++.h" #define int long long using namespace std; using ll = long long; using P = pair; //const ll INF = (1LL << 61); ll mod = 1000000007; struct mint { ll x; // typedef long long ll; mint(ll x = 0) :x((x%mod + mod) % mod) {} mint operator-() const { return mint(-x); } mint& operator+=(const mint a) { if ((x += a.x) >= mod) x -= mod; return *this; } mint& operator-=(const mint a) { if ((x += mod - a.x) >= mod) x -= mod; return *this; } mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this; } mint operator+(const mint a) const { mint res(*this); return res += a; } mint operator-(const mint a) const { mint res(*this); return res -= a; } mint operator*(const mint a) const { mint res(*this); return res *= a; } mint pow(ll t) const { if (!t) return 1; mint a = pow(t >> 1); a *= a; if (t & 1) a *= *this; return a; } // for prime mod mint inv() const { return pow(mod - 2); } mint& operator/=(const mint a) { return (*this) *= a.inv(); } mint operator/(const mint a) const { mint res(*this); return res /= a; } }; istream& operator>>(istream& is, mint& a) { return is >> a.x; } ostream& operator<<(ostream& os, const mint& a) { return os << a.x; } signed main() { ios::sync_with_stdio(false); cin.tie(0); int N; cin >> N; vectorA(N); for (int i = 0; i < N; i++)cin >> A[i]; mint now = 1; mint ans = 0; for (int i = 0; i < N - 1; i++) { now *= A[i]; ans += now * mint(3).pow(N - i - 2) * 2; } now *= A[N - 1]; ans += now; cout << ans << endl; return 0; }