#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
using mint = modint998244353;
const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	vector<int>a(n);
	long long sum = 0;
	rep(i, n) {
		cin >> a[i];
		if (0 == i % 2)sum += a[i];
		else sum -= a[i];
	}
	if (0 != sum % m) {
		cout << -1 << endl;
		return 0;
	}
	vector<mint>vx, vy;
	mint x = 1;//少数派
	mint y = 0;//多数派
	rep(i, n) {
		vx.push_back(x);
		vy.push_back(y);
		mint nx = y * (m - 1);
		mint ny = x + y * (m - 2);
		x = nx;
		y = ny;
	}
	mint ans = 0;
	sum = 0;
	rep(i, n - 1) {
		int r, l;
		if (0 == i % 2) {
			//[r,l)
			r = (sum + 0);
			l = (sum + a[i]);
			int  x = n - (i + 1);
			ans += (l - r) * vy[x];
			if (1 == x % 2) {
				if ((r <= (m - 1)) && ((m - 1) < l)) ans += vx[x] - vy[x];
			}
			else {
				if ((r <= (0)) && ((0) < l)) ans += vx[x] - vy[x];
			}
		}
		else {
			//(r,l]
			r = n - (sum + a[i]);
			l = n - (sum + 0);
			int  x = n - (i + 1);
			ans += (l - r) * vy[x];
			if (1 == x % 2) {
				if ((r < (-1)) && ((-1) <= l)) ans += vx[x] - vy[x];
				if ((r < (n - 1)) && ((n - 1) <= l)) ans += vx[x] - vy[x];
			}
			else {
				if ((r < (0)) && ((0) <= l)) ans += vx[x] - vy[x];
				if ((r < (n)) && ((n) <= l)) ans += vx[x] - vy[x];
			}
		}
		//cout << r << " " << l << endl;
		if (0 == i % 2) sum += a[i];
		else sum += m - a[i];
		sum %= m;
		//cout << ans.val() << endl;
	}
	ans++;
	cout << ans.val() << endl;
	return 0;
}