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

constexpr int mod = 998244353;

long long modpow(long long a,long long b) {
    long long ans = 1;
    while(b) {
        if(b & 1) {
            (ans *= a) %= mod;
        }
        (a *= a) %= mod;
        b /= 2;
    }
    return ans;
}

int main() {
    int N,M;
    cin >> N >> M;
    vector<int>A(N);
    int sum = 0;
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        if(i%2 == 0) {
            sum += A[i];
            sum %= M;
        }
        else {
            sum += M-A[i];
            sum %= M;
        }
    }
    if(sum != 0) {
        cout << -1 << endl;
        return 0;
    }
    vector<int>f(N+1);
    f[0] = 1;
    for(int i = 0; i < N; i++) {
        f[i+1] = f[i];
        if(i%2 == 0) {
            f[i+1] += mod-modpow(M-1,i+1);
            f[i+1] %= mod;
        }
        else {
            f[i+1] += modpow(M-1,i+1);
            f[i+1] %= mod;
        }
    }
    int res = 0,ans = 0;
    for(int i = 0; i+1 < N; i++) {
        int tmp = A[i]*modpow(M-1,N-i-2)%mod;
        if(i+2 < N) {
            int a = f[N-i-3];
            if((N-i-3)%2 == 0) {
                a = mod-a;   
            }
            tmp += 1ll*A[i]*a%mod;
            tmp %= mod;
        }
        if((N-i)%2 == 1 && (M-res)%M < A[i]) {
            tmp += 1;
            tmp %= mod;
        }
        if((N-i)%2 == 0 && (res+M-1)%M < A[i]) {
            tmp += mod-1;
            tmp %= mod;
        }
        ans += tmp;
        ans %= mod;
        if((N-i)%2 == 1) {
            res += A[i];
            res %= M;
        }
        else {
            res += M-A[i];
            res %= M;
        }
    }
    ans++;
    ans %= mod;
    cout << ans << endl;
}