#include using namespace std; using int64 = long long; // const int mod = 1e9 + 7; const int mod = 998244353; const int64 infll = (1LL << 62) - 1; const int inf = (1 << 30) - 1; struct IoSetup { IoSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } } iosetup; template< typename T1, typename T2 > ostream &operator<<(ostream &os, const pair< T1, T2 > &p) { os << p.first << " " << p.second; return os; } template< typename T1, typename T2 > istream &operator>>(istream &is, pair< T1, T2 > &p) { is >> p.first >> p.second; return is; } template< typename T > ostream &operator<<(ostream &os, const vector< T > &v) { for(int i = 0; i < (int) v.size(); i++) { os << v[i] << (i + 1 != v.size() ? " " : ""); } return os; } template< typename T > istream &operator>>(istream &is, vector< T > &v) { for(T &in : v) is >> in; return is; } template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); } template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); } template< typename T = int64 > vector< T > make_v(size_t a) { return vector< T >(a); } template< typename T, typename... Ts > auto make_v(size_t a, Ts... ts) { return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...)); } template< typename T, typename V > typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) { t = v; } template< typename T, typename V > typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) { for(auto &e : t) fill_v(e, v); } template< typename F > struct FixPoint : F { FixPoint(F &&f) : F(forward< F >(f)) {} template< typename... Args > decltype(auto) operator()(Args &&... args) const { return F::operator()(*this, forward< Args >(args)...); } }; template< typename F > inline decltype(auto) MFP(F &&f) { return FixPoint< F >{forward< F >(f)}; } #pragma GCC optimize ("O3") #pragma GCC target ("avx2") // or sse4 #pragma GCC optimize("unroll-loops") int main() { int N; cin >> N; vector< int > A(N); cin >> A; int dp[2501][2501] = {{}}; dp[N - 1][A[N - 1] - A[N - 2]] = 2; for(int i = N - 3; i >= 0; i--) { for(int j = i + 2; j < N; j++) { int64 sum = 0; for(int k = 0; k <= A[j] - A[i]; k++) { sum += dp[j][k]; } dp[i + 1][A[j] - A[i]] = sum % mod; for(int k = A[j] - A[i] + 1; k < 2501; k++) { dp[i + 1][k] = dp[j][k]; } } for(int j = i + 2; j < N; j++) { int64 sum = 0; for(int k = 0; k < A[i + 1] - A[i]; k++) { sum += dp[j][k]; dp[j][k] = 0; } dp[j][A[i + 1] - A[i]] += sum % mod; } } int64 ret = 0; for(int i = 0; i < N; i++) { for(int j = 0; j < 2501; j++) { ret += 1LL * dp[i][j] * j % mod; } } cout << ret << "\n"; }