#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <numeric>
#include <utility>
#include <tuple>

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
using ll = long long int;
using P = pair<ll, ll>;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; PPPPP(__VA_ARGS__); cerr << endl; } while(false)
template<typename T> void PPPPP(T t) { cerr << t; }
template<typename T, typename... S> void PPPPP(T t, S... s) { cerr << t << ", "; PPPPP(s...); }
#else
#define dump(...) do{ } while(false)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T> bool chmin(T &a, T b) { if (a > b) {a = b; return true; } return false; }
template<typename T> bool chmax(T &a, T b) { if (a < b) {a = b; return true; } return false; }
template<typename T> void print(T a) { cout << a << '\n'; }
template<typename T, typename... Ts> void print(T a, Ts... ts) { cout << a << ' '; print(ts...); }
template<typename T> istream &operator,(istream &in, T &t) { return in >> t; }
// clang-format on

template<ll MOD = 1000000007>
class ModInt {
    ll n;
    ModInt constexpr inverse() const {
        return ModInt::pow(*this, MOD - 2);
    }

public:
    ModInt()
        : n(0) {}
    ModInt(ll _n)
        : n(((_n % MOD) + MOD) % MOD) {}
    ModInt operator+=(const ModInt &m) {
        n += m.n;
        if (n >= MOD) n -= MOD;
        return *this;
    }
    ModInt operator-=(const ModInt &m) {
        n -= m.n;
        if (n < 0) n += MOD;
        return *this;
    }
    ModInt operator*=(const ModInt &m) {
        n *= m.n;
        if (n >= MOD) n %= MOD;
        return *this;
    }
    ModInt operator/=(const ModInt &m) {
        (*this) *= m.inverse();
        return *this;
    }
    friend ModInt operator+(ModInt t, const ModInt &m) {
        return t += m;
    }
    friend ModInt operator-(ModInt t, const ModInt &m) {
        return t -= m;
    }
    friend ModInt operator*(ModInt t, const ModInt &m) {
        return t *= m;
    }
    friend ModInt operator/(ModInt t, const ModInt &m) {
        return t /= m;
    }
    ModInt operator=(const ll l) {
        n = l % MOD;
        if (n < 0) n += MOD;
        return *this;
    }
    friend ostream &operator<<(ostream &out, const ModInt &m) {
        out << m.n;
        return out;
    }
    friend istream &operator>>(istream &in, ModInt &m) {
        ll l;
        in >> l;
        m = l;
        return in;
    }
    static constexpr ModInt pow(const ModInt x, ll p) {
        ModInt<MOD> ans = 1;
        for (ModInt<MOD> m = x; p > 0; p /= 2, m *= m) {
            if (p % 2) ans *= m;
        }
        return ans;
    }
};
using mint = ModInt<998244353>;
mint operator"" _m(unsigned long long m) {
    return mint(m);
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    cin, n;
    vector<int> a(n);
    rep(i, 0, n) {
        cin, a[i];
    }
    reverse(a.begin(), a.end());
    const int sz = 2501;
    mint ans = 0;
    mint prev = 0;
    rep(mx, a[0] - a[1], sz) {
        auto dp = make_v(n, 0_m);
        dp[1] = 2;
        int cur = 1;
        mint sum = 2;
        rep(i, 2, n) {
            if (a[i - 1] - a[i] > mx) {
                dp.assign(n, 0_m);
                break;
            }
            while (cur - 1 < n && a[cur - 1] - a[i] > mx) {
                sum -= dp[cur];
                cur++;
            }

            dp[i] += sum;
            sum += dp[i];
        }
        mint t = 0;
        rep(i, 1, n) {
            t += dp[i];
        }
        ans += mx * (t - prev);
        prev = t;
    }
    print(ans);

    /*
    dp[max][i][j];
    for max to 1 -> 2500 {
        dp1[max][i];
        int cur = 0;
        int sum = 0;
        
        for i to 1 -> n {
            while (abs(s[cur] - s[i]) > max) {
                sum -= dp1[max][cur];
                cur++;
            }
            if abs(s[i+1]-s[i]) > max {
                dp1[max][*] <- all 0
            }
            dp1[max][i] += sum;
            sum += dp1[max][i];

            for j to 1 -> i-1 {
                if abs(s[i+1]-s[j]) <= max {
                    dp1[max][i] <- dp1[max][j]
                }
            }
            
            for j to 1 -> i-1 {
                // 1..iまで追加されている
                // [max][i][j<i], [max][j<i][i]
                // i+1を追加する

                // 一番上のカードがi, j(<i)となっている
                // (i, j) -> (i+1, j), (i, i+1)
                // (j, i) -> (j, i+1), (i+1, i)
                // (i, j) == (j, i)
                // 最終的に答を2倍すればいい

                // これは次にコピーしているだけなので，省略可能
                if abs(s[i+1] - s[i]) <= max {
                    dp[max][i+1][j] += dp[max][i][j] 
                }
                
                // dp[max][i][i+1] = sum(dp[max][i][j]) for all j that abs(s[i+1] -a[j]) <= max and j <= i-1
                if abs(s[i+1] - s[j]) <= max {
                    dp[max][i+1][i] += dp[max][i][j]
                }
            }
        }
    }
    */
    return 0;
}