#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rep1(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < (t); ++i)
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define pob pop_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define newline puts("")
using namespace std;
template<typename T> using vc = vector<T>;
template<typename T> using vv = vc<vc<T>>;
template<typename T> using PQ = priority_queue<T,vc<T>,greater<T>>;
using uint = unsigned; using ull = unsigned long long;
using vi = vc<int>; using vvi = vv<int>; using vvvi = vv<vi>;
using ll = long long; using vl = vc<ll>; using vvl = vv<ll>; using vvvl = vv<vl>;
using P = pair<int,int>; using vp = vc<P>; using vvp = vv<P>;
int geti(){int x;scanf("%d",&x);return x;}
vi pm(int n, int s=0) { vi a(n); iota(rng(a),s); return a;}
template<typename T1,typename T2>istream& operator>>(istream&i,pair<T1,T2>&v){return i>>v.fi>>v.se;}
template<typename T1,typename T2>ostream& operator<<(ostream&o,const pair<T1,T2>&v){return o<<v.fi<<","<<v.se;}
template<typename T>istream& operator>>(istream&i,vc<T>&v){rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const T&v,const string& d=""){stringstream s;rep(i,sz(v))(i?s<<d:s)<<v[i];return s.str();}
template<typename T>ostream& operator<<(ostream&o,const vc<T>&v){if(sz(v))o<<join(v," ");return o;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int){a.fi--;a.se--;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int){a.fi--;a.se--;}
template<typename T>void operator--(vc<T>&a,int){for(T&x:a)x--;}
template<typename T>void operator++(vc<T>&a,int){for(T&x:a)x++;}
template<typename T>void operator+=(vc<T>&a,T b){for(T&x:a)x+=b;}
template<typename T>void operator+=(vc<T>&a,const vc<T>&b){a.insert(a.end(),rng(b));}
template<typename T1,typename T2>bool mins(T1& x,const T2&y){if(y<x){x=y;return true;}else return false;}
template<typename T1,typename T2>bool maxs(T1& x,const T2&y){if(x<y){x=y;return true;}else return false;}
template<typename Tx, typename Ty>Tx dup(Tx x, Ty y){return (x+y-1)/y;}
template<typename T>ll suma(const vc<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}
template<typename T>ll suma(const vv<T>&a){ll res(0);for(auto&&x:a)res+=suma(x);return res;}
template<typename T>void uni(T& a){sort(rng(a));a.erase(unique(rng(a)),a.end());}
template<typename T>void prepend(vc<T>&a,const T&x){a.insert(a.begin(),x);}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
#define dame { puts("-1"); return;}
#define yes { puts("Yes"); return;}
#define no { puts("No"); return;}
#define rtn(x) { cout<<(x)<<endl; return;}
#define yn {puts("Yes");}else{puts("No");}
const int MX = 200005;

// Mod int
// const uint mod = 1000000007;
const uint mod = 998244353;
struct mint {
  uint x;
  mint(): x(0) {}
  mint(ll x):x((x%mod+mod)%mod) {}
  mint operator-() const { return mint(0) - *this;}
  mint operator~() const { return mint(1) / *this;}
  mint& operator+=(const mint& a) { if((x+=a.x)>=mod) x-=mod; return *this;}
  mint& operator-=(const mint& a) { if((x+=mod-a.x)>=mod) x-=mod; return *this;}
  mint& operator*=(const mint& a) { x=(ull)x*a.x%mod; return *this;}
  mint& operator/=(const mint& a) { x=(ull)x*a.pow(mod-2).x%mod; return *this;}
  mint operator+(const mint& a) const { return mint(*this) += a;}
  mint operator-(const mint& a) const { return mint(*this) -= a;}
  mint operator*(const mint& a) const { return mint(*this) *= a;}
  mint operator/(const mint& a) const { return mint(*this) /= a;}
  mint pow(ll t) const {
    mint res = 1; for (mint p=x;t;p*=p,t>>=1) if (t&1) res *= p; return res;
  }
  mint ppow(ll t) const { int p=mod-1; return pow((t%p+p)%p);}
  bool operator<(const mint& a) const { return x < a.x;}
  bool operator==(const mint& a) const { return x == a.x;}
  bool operator!=(const mint& a) const { return x != a.x;}
};
mint ex(mint x, ll t) { return x.pow(t);}
istream& operator>>(istream&i,mint&a) {i>>a.x;return i;}
//*
ostream& operator<<(ostream&o,const mint&a) {o<<a.x;return o;}
/*/
ostream& operator<<(ostream&o, const mint&x) {
  int a = x.x, b = 1;
  rep(s,2)rep1(i,1000) {
    int y = ((s?-x:x)*i).x; if (abs(a)+b > y+i) a = s?-y:y, b = i;
  }
  o<<a; if (b != 1) o<<'/'<<b; return o;
}//*/
using vm = vector<mint>;
using vvm = vector<vm>;
struct modinv {
  int n; vm d;
  modinv(): n(2), d({0,1}) {}
  mint operator()(int i) { while (n <= i) d.pb(-d[mod%n]*(mod/n)), ++n; return d[i];}
  mint operator[](int i) const { return d[i];}
} invs;
struct modfact {
  int n; vm d;
  modfact(): n(2), d({1,1}) {}
  mint operator()(int i) { while (n <= i) d.pb(d.back()*n), ++n; return d[i];}
  mint operator[](int i) const { return d[i];}
} facs;
struct modfactinv {
  int n; vm d;
  modfactinv(): n(2), d({1,1}) {}
  mint operator()(int i) { while (n <= i) d.pb(d.back()*invs(n)), ++n; return d[i];}
  mint operator[](int i) const { return d[i];}
} ifacs;
mint comb(int a, int b) {
  if (a < b || b < 0) return 0;
  return facs(a)*ifacs(b)*ifacs(a-b);
}
struct modpow {
  mint x; int n; vm d;
  modpow(mint x=2): x(x), n(1), d(1,1) {}
  mint operator()(int i) { while (n <= i) d.pb(d.back()*x), ++n; return d[i];}
  mint operator[](int i) const { return d[i];}
} two(2);//, owt(invs(2));
//

struct Solver {
  void solve() {
    int n,m;
    scanf("%d%d",&n,&m);
    vi a(n);
    cin>>a;
    {
      int x = 0;
      rep(i,n) x = (a[i]-x+m)%m;
      if (x) dame;
    }
    vm s(n), t(n); vi u(n);
    s[n-1] = 0; t[n-1] = 1; u[n-1] = 0;
    drep(i,n-1) {
      s[i] = s[i+1]*(m-2)+t[i+1];
      t[i] = s[i+1]*(m-1);
      u[i] = (u[i+1]-1+m)%m;
    }

    mint ans = 1;
    rep(i,n) {
      mint now = s[i]*a[i];
      if (u[i] < a[i]) now += t[i]-s[i];
      ans += now;
    }
    cout<<ans<<endl;
  }
};

int main() {
  // cin.tie(nullptr); ios::sync_with_stdio(false);
  int ts = 1;
  // scanf("%d",&ts);
  rep1(ti,ts) {
    Solver solver;
    solver.solve();
  }
  return 0;
}