from collections import defaultdict

n = int(input())
A = list(map(int, input().split()))
mod = 998244353

ans = 0
N_cnt = defaultdict(int)
for i in range(n):
    a = A[i]
    N_cnt[a] += 1
C = [(num, cnt) for num, cnt in N_cnt.items()]
C.sort(key=lambda x: -x[0])
res = 0
ans = 0
for i in range(len(C) - 1):
    if C[i][0] - 1 == C[i + 1][0]:
        res += C[i][1]
        res %= mod
    else:
        res = 0
    ans += res
    ans %= mod
print(ans)