#include <stdio.h>

int main () {
  int n = 0;
  int m = 0;
  long long a[200000] = {};
  
  int res = 0;
  
  long long ans = 1LL;
  long long mod_num = 998244353LL;
  
  long long powm1[200000] = {};
  long long dp[200000][2] = {};
  
  long long sum = 0LL;
  int p = 0;
  
  res = scanf("%d", &n);
  res = scanf("%d", &m);
  for (int i = 0; i < n; i++) {
    res = scanf("%lld", a+i);
    sum += a[i];
  }
  
  if ((n <= 2 && a[0] != a[1]) || (n%2 == 0 && sum%2LL == 1LL)) {
    printf("-1\n");
    return 0;
  }
  
  if (n <= 2) {
    printf("%lld\n", a[0]+1LL);
    return 0;
  }
  
  if (n%2 == 1) {
    powm1[0] = 1LL;
    for (int i = 1; i < n; i++) {
      powm1[i] = (((long long) (m-1))*powm1[i-1]) % mod_num;
    }
    for (int i = 0; i < n; i++) {
      ans += powm1[n-i-1]*a[i];
    }
    printf("%lld\n", ans%mod_num);
    return 0;
  }
  
  dp[0][0] = 1LL;
  dp[0][1] = 0LL;
  for (int i = 1; i < n; i++) {
    dp[i][0] = dp[i-1][0]*((long long) (m/2));
    dp[i][0] = dp[i-1][1]*((long long) ((m-2)/2));
    dp[i][0] %= mod_num;
    dp[i][1] = dp[i-1][1]*((long long) (m/2));
    dp[i][1] = dp[i-1][0]*((long long) ((m-2)/2));
    dp[i][1] %= mod_num;
  }
  
  for (int i = 0; i < n; i++) {
    ans += ((long long) ((a[i]+1)/2))*dp[n-i-1][p];
    ans += ((long long) (a[i]/2))*dp[n-i-1][1-p];
    ans %= mod_num;
    if (a[i]%2LL == 1LL) {
      p = 1-p;
    }
  }
  
  printf("%lld\n", ans);
  return 0;
}