description: You are given an array of n positive integers a_1, a_2, …, a_n. Your task is to calculate the number of arrays of n positive integers b_1, b_2, …, b_n such that: 
  
    * 1 ≤ b_i ≤ a_i for every i (1 ≤ i ≤ n), and 
    * b_i ≠ b_{i+1} for every i (1 ≤ i ≤ n - 1). 
  
  
  
  The number of such arrays can be very large, so print it modulo 998 244 353.
  
  Input
  
  The first line contains a single integer n (1 ≤ n ≤ 2 ⋅ 10^5) — the length of the array a.
  
  The second line contains n integers a_1, a_2, …, a_n (1 ≤ a_i ≤ 10^9).
  
  Output
  
  Print the answer modulo 998 244 353 in a single line.
  
  Examples
  
  Input
  
  
  3
  2 2 2
  
  
  Output
  
  
  2
  
  Input
  
  
  2
  2 3
  
  
  Output
  
  
  4
  
  Input
  
  
  3
  1 1 1
  
  
  Output
  
  
  0
  
  Note
  
  In the first test case possible arrays are [1, 2, 1] and [2, 1, 2].
  
  In the second test case possible arrays are [1, 2], [1, 3], [2, 1] and [2, 3].
solution: import sys
  input=sys.stdin.readline
  
  mod=998244353
  
  n=int(input())
  L=list(map(int,input().split()))
  
  def solve(L):
      res=L[0]
      resmem=[L[0]]
      for i in range(1,len(L)):
          if L[i]>=L[i-1]:
              res*=(L[i]-1)
              res%=mod
              resmem.append(res)
          else:
              pt=i-1
              state=1
              while L[pt]>L[i]:
                  if pt==0:break
                  pt-=1
                  state*=-1
                  res+=state*resmem[pt]
                  res%=mod
              res*=L[i]
              res%=mod
              state*=-1
              if pt==0 and L[pt]>L[i]:
                  res+=L[i]*state
                  res%=mod
              else:
                  res+=resmem[pt]*state
                  res%=mod
              resmem.append(res)
      return res%mod
  
  print(solve(L))