def fairRations(B):
    odds = [i for i in range(len(B)) if B[i] % 2 == 1]
    bread = 0
    
    if (len(odds) % 2 == 1):
        return "NO"
    else:
        for j in range(0, len(odds)-1, 2):
            bread = bread + odds[j+1]-odds[j]
        
        return 2*bread

N = int(input())
B = list(map(int, input().split()))

result = fairRations(B)

print(result)