#include<bits/stdc++.h>
using namespace std;

#define INF 1234567890
#define ll long long
#define MOD 998244353

ll pw(ll a, ll n)
{
	ll ret = 1;
	while(n)
	{
		if (n&1) ret=ret*a%MOD;
		a=a*a%MOD;
		n >>= 1;
	}
	return ret;
}

ll inv(ll a)
{
	return pw(a, MOD-2);
}

int N, M;
int A[200201];

int main()
{
	ios::sync_with_stdio(0); cin.tie(0);
	cin.exceptions(ios::badbit | ios::failbit);
	cin >> N >> M;
	for(int i=1; i<=N; i++)
		cin >> A[i];

	ll res = 0; // (mod MOD)
	ll sum = 0; // (mod M)
	for(int i=1; i<=N; i++)
	{
		sum *= M-1, sum += A[i], sum %= M;
		res *= M-1, res += A[i], res %= MOD;
	}
	if (sum != 0) cout << "-1\n";
	else
	{
		res *= inv(M), res++;
		res %= MOD; res += MOD; res %= MOD;
		cout << res << "\n";
	}
	return 0;
}