#include using namespace std; using ll = long long; using pii = pair; template using V = vector; template using VV = V>; #define pb push_back #define eb emplace_back #define mp make_pair #define fi first #define se second #define rep(i, n) rep2(i, 0, n) #define rep2(i, m, n) for (int i = m; i < (n); i++) #define per(i, b) per2(i, 0, b) #define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--) #define ALL(c) (c).begin(), (c).end() #define SZ(x) ((int)(x).size()) constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); } template void chmin(T& t, const U& u) { if (t > u) t = u; } template void chmax(T& t, const U& u) { if (t < u) t = u; } template ostream& operator<<(ostream& os, const pair& p) { os << "(" << p.first << "," << p.second << ")"; return os; } template ostream& operator<<(ostream& os, const vector& v) { os << "{"; rep(i, v.size()) { if (i) os << ","; os << v[i]; } os << "}"; return os; } #ifdef LOCAL void debug_out() { cerr << endl; } template void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...); } #define debug(...) \ cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__) #define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl #else #define debug(...) (void(0)) #define dump(x) (void(0)) #endif template struct ModInt { using uint = unsigned int; using ull = unsigned long long; using M = ModInt; uint v; ModInt(ll _v = 0) { set_norm(_v % MOD + MOD); } M& set_norm(uint _v) { //[0, MOD * 2)->[0, MOD) v = (_v < MOD) ? _v : _v - MOD; return *this; } explicit operator bool() const { return v != 0; } M operator+(const M& a) const { return M().set_norm(v + a.v); } M operator-(const M& a) const { return M().set_norm(v + MOD - a.v); } M operator*(const M& a) const { return M().set_norm(ull(v) * a.v % MOD); } M operator/(const M& a) const { return *this * a.inv(); } M& operator+=(const M& a) { return *this = *this + a; } M& operator-=(const M& a) { return *this = *this - a; } M& operator*=(const M& a) { return *this = *this * a; } M& operator/=(const M& a) { return *this = *this / a; } M operator-() const { return M() - *this; } M& operator++(int) { return *this = *this + 1; } M& operator--(int) { return *this = *this - 1; } M pow(ll n) const { if (n < 0) return inv().pow(-n); M x = *this, res = 1; while (n) { if (n & 1) res *= x; x *= x; n >>= 1; } return res; } M inv() const { ll a = v, b = MOD, p = 1, q = 0, t; while (b != 0) { t = a / b; swap(a -= t * b, b); swap(p -= t * q, q); } return M(p); } bool operator==(const M& a) const { return v == a.v; } bool operator!=(const M& a) const { return v != a.v; } friend ostream& operator<<(ostream& os, const M& a) { return os << a.v; } static uint get_mod() { return MOD; } }; using Mint = ModInt<998244353>; template struct BIT { int n; vector bit; BIT(int _n = 0) : n(_n), bit(n + 1) {} // sum of [0, i), 0 <= i <= n T sum(int i) { T s = 0; while (i > 0) { s += bit[i]; i -= i & -i; } return s; } // 0 <= i < n void add(int i, T x) { ++i; while (i <= n) { bit[i] += x; i += i & -i; } } //[l, r) 0 <= l < r < n T sum(int l, int r) { return sum(r) - sum(l); } // not verified // smallest i, sum(i) >= w, none -> n + 1 int lower_bound(T w) { if (w <= 0) return 0; int x = 0, l = 1; while (l * 2 <= n) l *= 2; for (int k = l; k > 0; k /= 2) { if (x + k <= n && bit[x + k] < w) { w -= bit[x + k]; x += k; } } return x + 1; } }; const int MX = 2510; int main() { int N; cin >> N; V A(N); rep(i, N) cin >> A[i]; V ans(MX); int md = -1; rep(i, N - 1) chmax(md, A[i + 1] - A[i]); for (int d = md; d < MX; ++d) { V dp(N + 1); dp[0] = 2; for (int i = 1; i < N - 1; ++i) { Mint s; for (int j = 0; j < i - 1; ++j) { if (A[i] - A[j] <= d) { s += dp[j + 1]; } else { dp[j + 1] = 0; } } dp[i] = s + 2; } Mint s = 2; for (int j = 0; j < N - 1; ++j) { if (A[N - 1] - A[j] <= d) { s += dp[j + 1]; } } // debug(d, dp, s); ans[d] = s; } Mint a; for (int d = md; d < MX; ++d) { a += (ans[d] - ans[d - 1]) * d; } cout << a << endl; return 0; }