#include <stdio.h>

const int Mod = 998244353;

long long div_mod(long long x, long long y, long long z)
{
	if (x % y == 0) return x / y;
	else return (div_mod((1 + x / y) * y - x, (z % y), y) * z + x) / y;
}

long long pow_mod(int n, long long k)
{
	long long N, ans = 1;
	for (N = n; k > 0; k >>= 1, N = N * N % Mod) if (k & 1) ans = ans * N % Mod;
	return ans;
}

int main()
{
	int i, N, M, A[200001];
	scanf("%d %d", &N, &M);
	for (i = 1; i <= N; i++) scanf("%d", &(A[i]));
	
	long long B[200001];
	for (i = 1; i <= N; i++) B[i] = A[i];
	for (i = 1; i < N; i++) {
		if (B[i] % M == 0) continue;
		B[i+1] += M - B[i] % M;
		B[i] += M - B[i] % M;
	}
	if (B[N] % M != 0) {
		printf("-1\n");
		return 0;
	}
	
	int excep[2] = {0, M - 1};
	long long ans = 1, inv = div_mod(1, M, Mod);
	for (i = 1; i < N; i++) {
		if ((N - i) % 2 == 0) {
			ans += ((pow_mod(M - 1, N - i - 1) + 1) * (M - 1) % Mod * inv % Mod - 1) * A[i] % Mod;
			if (excep[1] - (A[i] - 1) < 0 || (excep[1] == M - 1 && A[i] > 0)) ans++;
			excep[0] -= A[i];
			excep[1] += A[i];
		} else {
			ans += ((pow_mod(M - 1, N - i - 1) - 1) * (M - 1) % Mod * inv % Mod + 1) * A[i] % Mod;
			if (excep[0] + A[i] - 1 >= M - 1) ans--;
			excep[0] -= A[i];
			excep[1] += A[i];
		}
		if (excep[0] >= M) excep[0] -= M;
		else if (excep[0] < 0) excep[0] += M;
		if (excep[1] >= M) excep[1] -= M;
		else if (excep[1] < 0) excep[1] += M;
	}
	printf("%lld\n", ans % Mod);
	fflush(stdout);
	return 0;
}