#include <iostream>
using namespace std;
typedef long long ll;

const ll MOD = 998244353;

int main()
{
    ll n, m;
    cin >> n >> m;
    ll a[200005];
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    ll s = 0, t = 0;
    for(int i = 0; i < n; i++)
    {
        s = s * (m - 1) + a[i];
        t = (t * (m - 1) + s / m) % MOD;
        s %= m;
    }
    if(s)
    {
        cout << -1 << endl;
    }
    else
    {
        cout << t + 1 << endl;
    }
}