import sys # sys.setrecursionlimit(200005) int1 = lambda x: int(x)-1 p2D = lambda x: print(*x, sep="\n") def II(): return int(sys.stdin.readline()) def LI(): return list(map(int, sys.stdin.readline().split())) def LLI(rows_number): return [LI() for _ in range(rows_number)] def LI1(): return list(map(int1, sys.stdin.readline().split())) def LLI1(rows_number): return [LI1() for _ in range(rows_number)] def SI(): return sys.stdin.readline().rstrip() # dij = [(0, 1), (-1, 0), (0, -1), (1, 0)] # dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)] # inf = 18446744073709551615 inf = 4294967295 # md = 10**9+7 md = 998244353 n = II() bb = LI() c = bb.count(-1) if n & 1: if c == 0: if bb[0] ^ bb[-1] == 1: ans = 1 else: ans = 0 elif bb[0] == -1 or bb[-1] == -1: ans = pow(2, c-1, md) elif bb[0] == bb[-1]: ans = 0 else: ans = pow(2, c, md) else: if c == 0: x = 0 for b in bb: x ^= b ans = x else: ans=pow(2,c-1,md) print(ans)