#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint998244353;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n, m; cin >> n >> m;
    vector<int> a(n);
    for(int i = 0; i < n; i++) cin >> a[i];
    int sum = 0;
    for(int i = 0; i < n; i++){
        if(i%2 == 0) sum += a[i];
        else sum -= a[i];
        sum %= m; sum += m; sum %= m;
    }
    if(sum != 0){
        cout << -1 << endl;
        return 0;
    }
    sum = 0;
    mint ans = 0;
    auto include = [&](int l, int r, int rem){
        if(r < l) swap(l, r);
        int x = l/m;
        for(int i = x-10; i <= x+10; i++){
            int y = i*m+rem;
            if(l <= y && y <= r) {
                return true;
            }
        }
        return false;
    };
    for(int i = 0; i < n; i++){
        int tail_len = n-i-1;
        mint tail_pat_all = mint(m-1).pow(tail_len);
        if(a[i] == 0) continue;
        if(tail_len%2 == 0){
            mint tail_ave = (tail_pat_all-1)/m;
            ans += a[i]*tail_ave;
            // 0が一つ多い
            if(i%2 == 0){
                if(include(sum, sum+a[i]-1, 0)) ans++;
            }else{
                if(include(sum, sum-(a[i]-1), 0)) ans++;
            }
        }else{
            mint tail_ave = (tail_pat_all+1)/m;
            ans += a[i]*tail_ave;
            // m-1が一つ少ない
            if(i%2 == 0){
                if(include(sum, sum+a[i]-1, m-1)) ans--;
            }else{
                if(include(sum, sum-(a[i]-1), 1)) ans--;
            }
        }
        if(i%2 == 0) sum += a[i];
        else sum -= a[i];
        sum %= m; sum += m; sum %= m;
    }
    cout << ans+1 << endl;
}