#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
import numpy as np
MOD = 10**9 + 7
# %%
M, *H = map(int, read().split())

# %%


def cumprod(A, MOD=MOD):
    L = len(A)
    Lsq = int(L**.5 + 1)
    A = np.resize(A, Lsq**2).reshape(Lsq, Lsq)
    for n in range(1, Lsq):
        A[:, n] *= A[:, n - 1]
        A[:, n] %= MOD
    for n in range(1, Lsq):
        A[n] *= A[n - 1, -1]
        A[n] %= MOD
    return A.ravel()[:L]


def make_fact(U, MOD=MOD):
    x = np.arange(U, dtype=np.int64)
    x[0] = 1
    fact = cumprod(x, MOD)
    x = np.arange(U, 0, -1, dtype=np.int64)
    x[0] = pow(int(fact[-1]), MOD - 2, MOD)
    fact_inv = cumprod(x, MOD)[::-1]
    fact.flags.writeable = False
    fact_inv.flags.writeable = False
    return fact, fact_inv


# %%
x = M - sum(H) - len(H) + 1
if x < 0:
    print('NA')
    exit()
if H[0] == 0:
    print(1)
    exit()
n = len(H) + 1


# %%
fact, fact_inv = make_fact(2 * 10 ** 6)
answer = fact[x + n - 1] * fact_inv[x] % MOD * fact_inv[n - 1] % MOD
print(answer)