#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 dp[200000][3] = {};
  
  long long sum[2] = {};
  long long tmp = 0LL;
  
  res = scanf("%d", &n);
  res = scanf("%d", &m);
  for (int i = 0; i < n; i++) {
    res = scanf("%lld", a+i);
    sum[i%2] += a[i];
  }
  
  if (sum[0]%m != sum[1]%m) {
    printf("-1\n");
    return 0;
  }
  
  dp[0][0] = 1LL;
  dp[0][1] = 1LL;
  dp[0][2] = 0LL;
  for (int i = 1; i < n; i++) {
    dp[i][0] = dp[i-1][0]+((long long) (m-2))*dp[i-1][1];
    dp[i][1] = dp[i-1][0]+dp[i-1][2]+((long long) (m-3))*dp[i-1][1];
    dp[i][2] = dp[i-1][2]+((long long) (m-2))*dp[i-1][1];
    dp[i][0] %= mod_num;
    dp[i][1] %= mod_num;
    dp[i][2] %= mod_num;
  }
  
  for (int i = 0; i < n-1; i++) {
    long long cnt = 0LL;
    if (a[i] > tmp) {
      ans += dp[n-i-2][0];
      cnt += 1LL;
    }
    if (tmp > 0LL && a[i] >= tmp) {
      ans += dp[n-i-2][2];
      cnt += 1LL;
    }
    ans += dp[n-i-2][1]*(a[i]-cnt);
    tmp = (((long long)m)-tmp+a[i])%((long long)m);
  }
  
  printf("%lld\n", ans%mod_num);
  return 0;
}