#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
ll ILL=2167167167167167167;
const int INF=2100000000;
const ll mod=998244353;
#define rep(i,a,b) for (ll i=a;i<b;i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}
template<class T> T min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T sum(vector<T> &a){assert(!a.empty());T ans=a[0]-a[0];for(auto &x:a) ans+=x;return ans;}

ll jyo(ll x,ll y,ll z){
  ll H=y; //ここから
       ll a=1,b=(x%z+z)%z,c=1;
       while(H>0){
         a*=2;
         if(H%a!=0){
           H-=a/2;
           c*=b;
           c%=z;
         }
        b*=b;
         b%=z;
      } //ここまで
 return c;
}



void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,0,t) solve();
}

void solve(){
	ll N,M;
	cin>>N>>M;
	vector<ll> A(N);
	rep(i,0,N) cin>>A[i];
	ll tmp=0;
	rep(i,0,N){
		if(i%2==0) tmp=tmp+A[i];
		else tmp-=A[i];
	}
	tmp=(tmp%M+M)%M;
	if(tmp!=0){
		cout<<"-1\n";
		return;
	}
	vector<ll> fact(N+1,1);
	rep(i,0,N) fact[i+1]=(fact[i]*(M-1))%mod;
	ll rev=jyo(M,mod-2,mod);
	ll ans=0;
	ll sum=0;
	rep(i,0,N){
		if((N-i)%2==1){
			ll base=((fact[N-i-1]-1)*rev)%mod;
			ans=(ans+base*A[i])%mod;
			tmp=(M-sum)%M;
			if(tmp<A[i]) ans++;
			sum=(sum+A[i])%M;
		}else{
			ll base=((fact[N-i-1]+1)*rev)%mod;
			ans=(ans+base*A[i])%mod;
			tmp=(sum-1+M)%M;
			if(tmp<A[i]) ans--;
			sum=(sum-A[i]+M)%M;
		}
		//cout<<sum<<" "<<ans<<"\n";
	}
	ans++;
	cout<<(ans%mod+mod)%mod<<"\n";
}