#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001
int n,m;
vector<int> c;

void dfs(int cur,int cv){
	if(cur==n){
		c[cv] ++;
		return;
	}
	rep(i,m-1){
		if(cur%2==0){
			dfs(cur+1,(cv+i)%m);
		}
		else{
			dfs(cur+1,(cv-i+m)%m);
		}
	}
}

bool check(int l,int r){
	if(l<=r){
		if(l<=1&&1<=r)return true;
	}
	else{
		if(r>=1)return true;
	}
	return false;
}


int main(){
	
	
	cin>>n>>m;
	/*
	c.resize(m,0);
	dfs(0,0);
	
	rep(i,m){
		cout<<c[i]<<endl;
	}
	*/
	
	vector<int> a(n);
	int s= 0 ;
	rep(i,n){
		cin>>a[i];
		if(i%2==0){
			s += a[i];
		}
		else{
			s += m-a[i];
		}
		s %= m;
	}
	if(s!=0){
		cout<<-1<<endl;
		return 0;
	}
	
	
	mint ans = 1;
	
	s = 0;
	
	rep(i,n){
		if(a[i]!=0){
			int l,r;
			if(i%2==0){
				l = s;
				r = s+a[i]-1;
				r %= m;
			}
			else{
				r = s;
				l = s - (a[i]-1) + m;
				l %= m;
			}
			//cout<<l<<','<<r<<endl;
			int remain = n-1-i;
			if(remain%2==0){
				mint t = mint(m-1).pow(remain)-1;
				t /= m;
				ans += t * a[i];
				
				if(l==0||l>r)ans++;
				//if(check(l,r))ans++;
			}
			else{
				mint t = mint(m-1).pow(remain)+1;
				t /= m;
				ans += t * a[i];
				if(check(l,r))ans--;
				//if(r==m-1 || l>r)ans--;
			}
		}
		
		if(i%2==0){
			s += a[i];
		}
		else{
			s += m-a[i];
		}
		s %= m;
	}
	//ans++;
	cout<<ans.val()<<endl;
	
	return 0;
}