#define _USE_MATH_DEFINES #include using namespace std; #define FOR(i,m,n) for(int i=(m);i<(n);++i) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() using ll = long long; constexpr int INF = 0x3f3f3f3f; constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL; constexpr double EPS = 1e-8; constexpr int MOD = 1000000007; // constexpr int MOD = 998244353; constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1}; constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1}; template inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; } template inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; } struct IOSetup { IOSetup() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << fixed << setprecision(20); } } iosetup; template struct MInt { unsigned val; MInt(): val(0) {} MInt(long long x) : val(x >= 0 ? x % MOD : x % MOD + MOD) {} static int get_mod() { return MOD; } static void set_mod(int divisor) { assert(divisor == MOD); } MInt pow(long long exponent) const { MInt tmp = *this, res = 1; while (exponent > 0) { if (exponent & 1) res *= tmp; tmp *= tmp; exponent >>= 1; } return res; } MInt &operator+=(const MInt &x) { if((val += x.val) >= MOD) val -= MOD; return *this; } MInt &operator-=(const MInt &x) { if((val += MOD - x.val) >= MOD) val -= MOD; return *this; } MInt &operator*=(const MInt &x) { val = static_cast(val) * x.val % MOD; return *this; } MInt &operator/=(const MInt &x) { // assert(std::__gcd(static_cast(x.val), MOD) == 1); unsigned a = x.val, b = MOD; int u = 1, v = 0; while (b) { unsigned tmp = a / b; std::swap(a -= tmp * b, b); std::swap(u -= tmp * v, v); } return *this *= u; } bool operator==(const MInt &x) const { return val == x.val; } bool operator!=(const MInt &x) const { return val != x.val; } bool operator<(const MInt &x) const { return val < x.val; } bool operator<=(const MInt &x) const { return val <= x.val; } bool operator>(const MInt &x) const { return val > x.val; } bool operator>=(const MInt &x) const { return val >= x.val; } MInt &operator++() { if (++val == MOD) val = 0; return *this; } MInt operator++(int) { MInt res = *this; ++*this; return res; } MInt &operator--() { val = (val == 0 ? MOD : val) - 1; return *this; } MInt operator--(int) { MInt res = *this; --*this; return res; } MInt operator+() const { return *this; } MInt operator-() const { return MInt(val ? MOD - val : 0); } MInt operator+(const MInt &x) const { return MInt(*this) += x; } MInt operator-(const MInt &x) const { return MInt(*this) -= x; } MInt operator*(const MInt &x) const { return MInt(*this) *= x; } MInt operator/(const MInt &x) const { return MInt(*this) /= x; } friend std::ostream &operator<<(std::ostream &os, const MInt &x) { return os << x.val; } friend std::istream &operator>>(std::istream &is, MInt &x) { long long val; is >> val; x = MInt(val); return is; } }; namespace std { template MInt abs(const MInt &x) { return x; } } template struct Combinatorics { using ModInt = MInt; int val; // "val!" and "mod" must be disjoint. std::vector fact, fact_inv, inv; Combinatorics(int val = 10000000) : val(val), fact(val + 1), fact_inv(val + 1), inv(val + 1) { fact[0] = 1; for (int i = 1; i <= val; ++i) fact[i] = fact[i - 1] * i; fact_inv[val] = ModInt(1) / fact[val]; for (int i = val; i > 0; --i) fact_inv[i - 1] = fact_inv[i] * i; for (int i = 1; i <= val; ++i) inv[i] = fact[i - 1] * fact_inv[i]; } ModInt nCk(int n, int k) const { if (n < 0 || n < k || k < 0) return 0; assert(n <= val && k <= val); return fact[n] * fact_inv[k] * fact_inv[n - k]; } ModInt nPk(int n, int k) const { if (n < 0 || n < k || k < 0) return 0; assert(n <= val); return fact[n] * fact_inv[n - k]; } ModInt nHk(int n, int k) const { if (n < 0 || k < 0) return 0; return k == 0 ? 1 : nCk(n + k - 1, k); } }; using ModInt = MInt; // https://codeforces.com/contest/1461/problem/F ModInt solve(vector a) { int n = a.size(); if (n == 1) return a[0]; if (n == 2) return 1LL * a[0] * a[1]; vector mul(n); mul[0] = a[0]; FOR(i, 1, n) mul[i] = min(mul[i - 1] * a[i], 1LL * INF); if (mul[n - 1] == INF) { ModInt res = 1; for (int e : a) res *= e; return res; } vector b; for (int i = 0; i < n;) { int j = i + 1; if (a[i] == 1) { while (j < n && a[j] == 1) ++j; b.emplace_back(j - i); } else { int mul = a[i]; while (j < n && a[j] > 1) mul *= a[j++]; b.emplace_back(mul); } i = j; } int m = b.size(); assert(m % 2 == 1); vector dp(m, -LINF); vector prev(m, -1); dp[0] = b[0]; prev[0] = 0; for (int i = 2; i < m; i += 2) { dp[i] = dp[i - 2] + b[i - 1] + b[i]; prev[i] = i; int mul = b[i]; for (int j = i - 2; j >= 0; j -= 2) { mul *= b[j]; if (dp[i] < (j == 0 ? 0 : dp[j - 2] + b[j - 1]) + mul) { dp[i] = (j == 0 ? 0 : dp[j - 2] + b[j - 1]) + mul; prev[i] = j; } } } int pos = m - 1; vector plus(m, true); while (pos >= 0) { FOR(i, prev[pos], pos) plus[i] = false; pos = prev[pos] - 2; } string ans = ""; bool ast = true; for (int i = 0, idx = 0; i < n; ++idx) { int j = i; if (a[i] == 1) { while (j < n && a[j] == 1) { ans += ast ? '*' : '+'; ++j; } } else { while (j < n && a[j] > 1) { ans += '*'; ++j; } ans.pop_back(); ast = !plus[idx]; ans += ast ? '*' : '+'; } i = j; } ans.pop_back(); ModInt res = 0, cur = a[0]; for (int i = 1; i < n; ++i) { if (ans[i - 1] == '+') { res += cur; cur = a[i]; } else if (ans[i - 1] == '*') { cur *= a[i]; } } return res + cur; } int main() { int n; cin >> n; vector a(n); REP(i, n) cin >> a[i]; ModInt ans = 0; for (int i = 0; i < n;) { if (a[i] == 1) { ans += a[i++]; continue; } int j = n - 1; while (j >= i && a[j] == 1) --j; ans += solve(vector(a.begin() + i, a.begin() + j + 1)); ans += n - (j + 1); break; } cout << ans << '\n'; return 0; }