def fairRations(B):
    # Write your code here
    c = 0
    n = len(B)
    for i in range(n - 1):
        if B[i] % 2 != 0:
            B[i + 1] += 1
            c += 2
            
    return "NO" if B[-1] % 2 != 0 else str(c)