#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic pop
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

struct S {
  int cnt;
  mint s;
};

S op(S x, S y) { return {x.cnt + y.cnt, x.s + y.s}; }
S e() { return {0, 0}; }

struct F { mint a, b; };
F composition(F f, F g) {
  return {f.a * g.a, f.a * g.b + f.b};
}
F id() { return {1, 0}; }

S mapping(F f, S x) { return {x.cnt, f.a * x.s + f.b * x.cnt}; }

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  VI a(n), d(n + 1);
  rep(i, n) cin >> a[i];
  {
    int r = 0;
    rep(i, n) {
      r += i % 2 == 0 ? a[i] : -a[i];
      r %= m;
      if (r < 0) r += m;
      d[i+1] = r;
    }
    if (r) {
      cout << -1 << '\n';
      return 0;
    }
  }
  lazy_segtree<S, op, e, F, mapping, composition, id> seg(vector<S>(m, S{1, 0}));
  seg.set(0, S{1, 1});
  int base = 0;
  mint ans;
  // rep(i, n + 1) cout << d[i] << " \n"[i + 1 == n + 1];
  rrep(i, n) {
    int lb = i % 2 == 0 ? base + d[i] : base + d[i] - a[i] + 1;
    lb %= m;
    int ub = lb + a[i];
    ans += seg.prod(lb, min(ub, m)).s;
    ans += seg.prod(0, max(ub - m, 0)).s;
    // cout << i << ' ' << lb << ' ' << ub << ' ' << ans.val() << '\n';
    mint tot = seg.all_prod().s;
    seg.apply(0, m, F{-1, tot});
    if (i % 2 == 1) {
      base++;
      if (base == m) base = 0;
    } else {
      base--;
      if (base == -1) base = m - 1;
    }
    // cout << endl;
    // rep(i, m) {
    //   int r = (i + base)% m;
    //   cout << seg.get(r).s.val() << " \n"[i + 1 == m];
    // }
  }
  ans++;
  cout << ans.val() << '\n';
}